What are the benefits for a Harengon to be Small instead of Medium?

Question

The Harengon race in The Wild Beyond the Witchlight, along with many other races says:

You are Medium or Small. You choose the size when you select this race.

Besides the Squat Nimbleness feat and minimum size of mount, what are the differences, mechanically, that would help you decide which to pick?

Answer 1

There is a few differences but nothing that would specifically affect only Harengon

Apart from the Squat Nimbleness feat (which is restricted to Small creatures) and mount rules here are the other differences that I am aware of:

• Grappling and Shoving: you can grapple or shove a creature that is at most 1 size larger than you, so Medium characters can grapple or shove creatures that are up to Large in size, whereas a Small one can only grapple or shove Medium sized or smaller.
• Heavy weapons: If a weapon has the “heavy” property, Small creatures attack with it at Disadvantage.
• Moving through hostile creature’s space: the creature needs to be at least 2 sizes smaller or larger for you to be able to move through its space so a Small character can move through Large creature’s space, whereas for a Medium character the creature must be Huge to allow this; however, Medium character can move through Tiny creature’s space and a Small character cannot.
• Squeezing: Small characters can get into spaces that Medium characters wouldn’t fit in at all. Since you can Squeeze into a space that’s big enough for a creature 1 size smaller than you, and RAW both Medium and Small creatures occupy 5x5 ft., Small creatures can Squeeze into Tiny spaces, whereas Medium creatures effectively cannot squeeze. Note: this is a strict RAW interpretation, in practice a lot of DMs treat squeezing rules differently.*
• Being smaller means more opportunities for hiding and for cover since you can use a smaller object to do so.
• A Small creature is usually lighter than a Medium one, that can help you avoid traps of the structure “X happen if more than Y pounds of weight is put on it”, of which there are multiple instances in official campaigns - rotten floorboards, rigged bridges, pressure plates, etc.
• Dimension Door: the spell allows you to bring along one creature of your size or smaller, as a Small PC you would not be able to take a Medium party member with you

Which one is better is quite relative as it depends on what sort of character you are planning to play, e.g. for a rogue being Small would probably be quite beneficial, allowing you to make use of all sorts of hidey-holes, whereas for a Greatsword-wielding Fighter it would just be a detriment.