Note that Physics is an exception. By default it does not use dt, and therefore is framerate dependent. This is because dt usually has small random variations. These variations can make the same setup in a physics game give different results even if exactly the same thing is done twice. This is often annoying for physics games, so by default it is framerate dependent.
What can I expect from a square or ball-sprite with "set stepping to framerate independant" set to on and a ball-sprite set to "fixed"?
Only: prepare to see possible different movement everytime the layout is run?
Are there other things to keep in mind when choosing for one or the other option?