In the 2024 rules, Small creatures no longer have Disadvantage making attacks with Heavy weapons (unless their Strength [for melee] or Dexterity [for ranged] is <13).
Small had no effect on Versatile weapons or on Carrying Capacity in the 2014 rules and still doesn’t.
Being Small does affect movement around creatures in combat, as you can move through the space of a hostile creature if it is two sizes larger or smaller than you (so a Small creature can move through the space of a Large enemy, whereas a Medium can not).
Also, you can use a creature as a mount if it is at least one size larger than you.
The DM can also define openings as being large enough for a Small creature but too small for a Medium.
Your size is also used in the Difficult Terrain rules for another detail:
A space is Difficult Terrain if the space contains any of the following or something similar:
A creature that isn’t Tiny or your ally (already mentioned byThelenyiWhinlaw)
Furniture that is sized for creatures of your size or larger
Heavy snow, ice, rubble, or undergrowth
Liquid that’s between shin- and waist-deep
A narrow opening sized for a creature one size smaller than you (already mentioned byThelenyiWhinlaw)
A slope of 20 degrees or more
Some drawbacks for being small:
High Jump: "You can extend your arms half your height above yourself during the jump. Thus, you can reach a distance equal to the height of the jump plus 1½ times your height."
Prone Condition if ending your turn in the same space as a Small or Medium creature
You cannot grapple or shove Large creatures using Unarmed Strikes
Interaction between Grappled [Condition] and Large creatures vs Small ones: "The grappler can drag or carry you when it moves, but every foot of movement costs it 1 extra foot unless you are Tiny or two or more sizes smaller than it."
So in the most recent rules, what does being Small actually affect?
Weapons? Versatile? Heavy?
Carrying capacity?
Anything?
In the 2024 rules, Small creatures no longer have Disadvantage making attacks with Heavy weapons (unless their Strength [for melee] or Dexterity [for ranged] is <13).
Small had no effect on Versatile weapons or on Carrying Capacity in the 2014 rules and still doesn’t.
Being Small does affect movement around creatures in combat, as you can move through the space of a hostile creature if it is two sizes larger or smaller than you (so a Small creature can move through the space of a Large enemy, whereas a Medium can not).
Also, you can use a creature as a mount if it is at least one size larger than you.
The DM can also define openings as being large enough for a Small creature but too small for a Medium.
Your size is also used in the Difficult Terrain rules for another detail:
Some drawbacks for being small:
Oh, also Cover is related to your height, so being Small is actually an advantage in this case: