For what we need thigh_twist and calf_twist in epic skeleton?

Good day. I wonder about the purposes for thigh_twist and calf_twist in default skeleton. Why we need them? As i can see, if I move it - nothing happens. They’re placed within other bones and do nothing (as I can see):

we have lowerarm_twist and I thought it shouldn’t affect on mesh just like thigh and calf twist, but it does:

Why? Can anybody explain me the purpose of that bones? I need to know it because I want to create armature in Blender, load it in ue5 and keep it compatible with epic skeleton, but I don’t want just export skeleton from unreal, I want to understand it.

these bones are needed for proper deformation of the arms and legs. This is about how weights should be done

Forget the epic skeleton. it’s sheer trash.
Do your thing. Re-target later.