A way to test an avatar's movement before you upload to make sure nothing is conflicting animation wise! On older avatars, they are not easily compatible with gogo loco and other such prefabs, and putting them on the avatar breaks the leg rigging. Having a way to test the rigging using the standard VRChat movements within the Unity SDK would help with having to continuously reupload avatars to test animations. A simple walk, run, crouch, and prone animation would do wonders to make sure the rigging works on older models, and to see if bones need to be redone due to in-ward or outward knee bending!