SAS works fine for pointing the right way, but doesn't do much for roll (other than stabilizing it).
For rockets roll doesn't really matter, but for planes it does, and I often find myself busy finetuning the roll so that my wings are nice and level. While SAS could do that as well. So my suggestion: add an option for prograde and wings level, and/or for stabilize pitch, while nulling yaw and roll (useful if you want to keep pitch up a few degress).