Good to know. How do you happen to know it?

The mission the PCs are on could be a direct assault on a stronghold that would distract the occupants/enemy from someone else sneaking in (or out). A running battle (using whatever tactics are available, etc.) could work if it keeps the enemy attention away from a specific location/area in the stronghold. The enemy forces would hopefully still be divided by not all fighting them at once. People often want a different setting once in a while, but a different kind of adventure can work, too, in my opinion.

How do I know about asymmetrical warfare?  It's not an obscure concept, the US has been in one for the last 19 years.

The biggest impediment to successful use of guerrilla warfare is that most parties are made up of players and/or characters who have vastly different capabilities, aptitudes, and attitudes.  In most parties, stealth isn't priority skill for everyone and neither is movement speed nor the Mobile feat.  A really successful use of hit-and-run or feint-trap-and-flank would require the entire party to be on the same page about the value of the tactic and be willing to follow orders.  The typical initiative rules also work against well coordinated guerrilla tactics because initiative is entirely random, rending sequential battle plans largely moot.

Also, I'm a little surprised that no one here has mentioned mounted combat in the context of guerrilla warfare.  The high move speed of most mounts and the capability to have the mount disengage for the PC are invaluable to hit-and-run tactics.  The Mongolian Empire combined mounted archery and cavalry with much success, for instance.  

The Mongols were excellent at mobile warfare.  They were terrible at guerrilla warfare- horses aren't remotely stealthy, especially not in groups.

Guerrilla warfare does not always necessitate stealth in the conventional D&D sense.  Having a small group of cavalry  springing a boulder trap on the enemy's supply wagons and then retreating on horseback is still guerrilla warfare.   So is using that same small group of cavalry to attack the encamped enemy position, setting fire to tents and running away.  It's possible for horses to not be galloping on their approach to the enemy position so long as you plan well enough in advance and have greater familiarity with terrain, chokepoints, etc. than the opposing side.  

Quote from Song_of_Blues >>

The biggest impediment to successful use of guerrilla warfare is that most parties are made up of players and/or characters who have vastly different capabilities, aptitudes, and attitudes.  In most parties, stealth isn't priority skill for everyone and neither is movement speed nor the Mobile feat.  A really successful use of hit-and-run or feint-trap-and-flank would require the entire party to be on the same page about the value of the tactic and be willing to follow orders.  The typical initiative rules also work against well coordinated guerrilla tactics because initiative is entirely random, rending sequential battle plans largely moot.

  

 Yeah, my Cleric is the roadblock on this plan, LOL. I have DEX and STR as 8 and always wear armour with Stealth Disadvantage. Only my DM complains about it once in awhile. He just can't visualize a caster cleric with high AC and HP. I still wade in and out of combat as I chose, I just don't do it quietly and I don't physically hit things.  

Well, different strokes for different folks.  Optimizing for tactical efficiency isn't on the minds of a lot of players.  While I see it's value, I tend to go for interesting character concepts myself over what is the most powerful build.  I also have no control over what characters other people want to play, so it's tricky trying to aim for surprise as a reliable method of approach even if I wanted to.  

Quote from Brian_Avery >>

I don't know why everyone isn't always trying to surprise your foes, a free round of attacks sounds pretty good to me.

 Constantly ambushing enemies is an inherently dishonorable act to some folk's moral compass. My partyHAS ambushed some giants but, they can one shot you with a crit so, yeah.

What is being described in this thread is not guerrilla warfare.  It is mostly a combination of Fire-and-Maneuver and Ambush.  Guerrilla Warfare is an approach to war on a higher level than tactics.  Generally you use small units to attack an opponents Command and Control, Communications, Logistics and too often civilians, a fine line before you cross over into terrorism.  You attempt to weaken the government while attempting to organize an uprising among the populace.

if you are destroying supplies, or destroying their camping equipment and making their horses panic and run away, that is certainly a disruption to logistics and control.  It it is not necessarily guerrilla warfare in and of itself,  that does not in any way mean that it could not be part of a larger strategy to slow down and eventually eliminate the enemy.  

Also, going by your emphasis on strategy (as opposed to tactics), MusicScout, most PCs would never be able to engage in guerrilla warfare b/c D&D is not primarily a war game.  It was originally inspired by war games, but in its current iteration does not function in that regard.  Grand strategy is not something facilitated by the initiative rules and focus on individual PCs.  We might as well be talking about WarHammer instead because that is actually designed as a war game.  

The obvious reason to believe that you need to use a Hide action is because certain classes and monsters (e.g. the goblin) have special abilities designed to enable this sort of tactic, and they wouldn't have those abilities if they weren't needed.

On the issue 'war game', war games come in different magnitudes; combat in most RPGs is essentially a squad-level tactical wargame, which is the smallest scale, and it proceeds from there through multiple scales up to grand strategy at the top.

Skipping all the invisibility vs. hiding vs. senses stuff, because its all been argued over before and the rules as written are so inconsistent that it's hard to suss out whether the RAW and RAI don't match or whether the system is working as intended but wasn't sufficient edited/playtested enough to be coherent in the first plac. Focusing instead on a couple posts up...

 Quote from MusicScout >>

Guerrilla Warfare is an approach to war on a higher level than tactics.  Generally you use small units to attack an opponents Command and Control, Communications, Logistics and too often civilians, a fine line before you cross over into terrorism.  You attempt to weaken the government while attempting to organize an uprising among the populace.

 This, and it's so fun when players do it, or when (weak) monsters do it to the party! Figuring out how you want to fight and kill the Lich is one thing, and may either take up a single encounter or possibly a few weeks of adventure time. But organizing a guerilla resistance movement against a superior and unstoppable undead army? Sneaking around the countryside to assassainate his necromancer generals, destroying the sources of power that sustain his army, razing the horrible factories and foundries that equip his minions? That's guerilla warfare, and it's the sort of thing that can shape an entire campaign.

Or flipped around, the party is moving through Kobold territory, big yawn usually because Kobolds suck. But Kobolds know they suck, and furthermore they're cowards that don't respond to sucking by just throwing endless waves of bodies at their problems. They build traps, and false passages with cave ins, and murder holes, and escape routes, and backup escape routes, and etc etc etc.... in my mind, fighting kobolds on their own turf should always feel like fighting the worst most unfair protracted fight against a phantom force, where you may get through 5 or 6 "encounters" with the lil' bastards before you ever finally actually manage to see one in the flesh (and then promptly realize it was an illusion designed to lure you over a collapsing pit trap). And yes, that's starting to slip back into 'tactics'... but extrapolate that into what it means for a civilized population when it butts up against a kobold warren, how differently kobolds wage war against villagers vs. goblins vs. orcs.... 

Nobody likes a fair fight, except for Lawful Stupid paladins. Maximizing strength and minimizing risk extends beyond what you do in combat, but also what combats you seek out against what targets and when, and it's very fun to dive into that layer of strategy for players and respond to it when used against them.