Besides the things which are listed in the spell's description (namely turning some nearby trees into a non-improvised quality bridge in just 10 minutes time - which is very useful for crossing ravines or bodies of water full of dangers), I've seen the spell get a few good uses that made a difference to the story.
In one campaign, it helped the party build (and rebuild) airships faster than they otherwise would be able to, which was significantly helpful towards their intermingled goals of inventing an entirely non-magical airship, deceiving the empire they were funded by into thinking slow-moving dirigible blimps were that absolute best that could be achieved, and getting their own vastly superior airship assembled and fully operational (and hidden elsewhere) before imperial agents came back for another quarterly progress report.
In another, it (and other spells, like stone shape) helped the party establish a fortified stronghold.
Of course, those were in prior editions where the spell was a little more potent in its potential effects, but for the most part they would still work in 5th edition, they'd just take more numerous castings of the spell for things like turning trees into lumber.
When we got into places where we could summon beasts of burden we fabricated carts and tack.
In swamps we fashioned swamp shoes and sledges to spread out body weight so we were less likely to get mired.
This all had a massive effect as we never had to keep any of this survival gear. We simply fabricated it with left over slots the night before and ditched the mode of transportation when it became inconvenient.
Basically it changed our route through the jungles to a more direct route and it changed encounters as we could avoid swarms of undead and large beasts like t-rex'es by being on the water.
Also by being on a boat or in a cart delicate casters could rest while the rest of the party was still driving towards our goals.
We also fabricated barricades at one point when we decided a place was a good place to set up a multi-day camp.
All this being said I really wish this spell had the option to be cast as a ritual with expensive re usable components rather than being just a 4th level spell.
The most game breaking idea I can think of for fabricate is probably just using it to keep a necromancers skeletons in arrows and armor. Which granted is a lot of DPR but it's really dull if all your doing all game is swarm management.
-In a fight there was a baddie behind a thick wall of ice that was surrounded by difficult terrain. Instead of marching my skeletons around it, I used fabricate to turn a large chunk of the ice wall into water so that my skeletons had a direct line of sight to shoot.
-Fabricate was nice to create spare wheels/axles for our wagon when needed.
-For the spell 'Soul Cage' you need a silver cage worth 100g, so I took 1000 silver coins and used fabricate because I wasn't near any towns at the time and had just learned the spell. (Whether coin currency can be used as 'raw' material is up to DM interpretation)
-Used Fabricate to create fancy clothes (could probably do disguises as well), so long as your DM does not interpret that any advanced tailoring skills are needed.
-Fabricate to create a bridge out of logs to cross a river.
I'm sure there's a whole load more, the in combat uses are minimal, but out of combat the spell really shines.