The point is: At the time layers was written, the CPU was slow, the blitter was fast, and chipmem was an expensive resource. Thus, layers was designed with these goals in mind: Use as little buffer memory as possible, probably of the expense of additional data manipulations to be made by the fast blitter.
Don't know. Hidden parts of smart refresh layers may end up being backed up in offscreen bitmaps three times. If there is an installed clipregion and the layer is in BeginUpdate state.
Instead it would have been better to just add some offsetx,offsety fields to cliprect struct so that if layer has clipregion installed and/or is in in beginupdate state the normal "hidden cliprect offscreen bitmaps" can be reused.
