you make one body
round the edges
split the body into two.
now with offset face you can:
offset - change the sides of the body individually
But you cannot:
with offset adjust the just the fillet radious of a split body
it will adjust in the timeline the first fillet value for the complete body
VIDEO: https://drive.google.com/file/d/0Byzv_NlyKp_2aVRZUDdhZk0taDQ/view
this is really needed when you want to shrink a body including the fillet - currently with fusion I cannot make correctly smaller edges.
when rounded edges are at an angle