What does the use_local_location mean for bones To test this, I run a test to show the difference of use local location or not. 


  
    
      C.object.data.bones['upperArm.R'].use_local_location = False
      C.object.data.bones['upperArm.R'].head
      Vector((-0.1459999978542328, -0.014370977878570557, -0.0010000000474974513))
      
      C.object.data.bones['upperArm.R'].head_local
      Vector((-0.1459999978542328, 0.0010000000474974513, 0.43700000643730164))
      
      C.object.data.bones['upperArm.R'].use_local_location = True
      C.object.data.bones['upperArm.R'].head_local
      Vector((-0.1459999978542328, 0.0010000000474974513, 0.43700000643730164))
      
      C.object.data.bones['upperArm.R'].head
      Vector((-0.1459999978542328, -0.014370977878570557, -0.0010000000474974513))
    
  


It comes out help nothing in the coordinates. Everything stays the same after and before setting the local location. At least, the coordinate will be different after changing the coordinate system. 

Can someone provide some insight into this?
Apparently this setting only affects the way the location coordinates are displayed on the Transform properties on the UI.

When True, coordinates are shown using the bone local space.

When False, coordinates are shown using the parent space. (Global for the root bone)

Also note this only appears to affect POSED bones and has no effect when editing bones.

Also this can only be set on unconnected bones.