Better voices for males as someone already mentioned. The main thing though, for me anyway, is body changes. It breaks my immersion to see Halsin as an elf flexing around camp. It also bothers me that fighters and probably barbarians would be the same size as a wizards and other pure spellcasters. Half casters I could understand but come on.
I could guess it has to do with mesh codes, but whatever. Let my martial classes actually look like they can fight in melee.
Look at Githyanki as a warrior and you will see how stupidly he looks in armor.
Yeah armor meshs are a pain to deal with. Personally I wont even bother with Githyanki. None baddass iconic hair and facial hair. So far none of the unique variations of Gith armor for males. The books have way better versions of Laezel's armor for males too. Even though they may not make it in, Githzarai have amazing cloths and armor. Githzarai would be the only way I'd consider playing a monk.
Female Gith benefit from the skinny look while the males suffer greatly. Gith have to be skinny, but I wish Larian would use that "creative freedom wiggle room" to help them out.