Here's what I got: an ancient small bath with the overhead light switch by the sink. We're adding a GFCI outlet, and since the switch for the vanity light we're also adding is in the same box, we should protect the vanity light circuit because it's easy to do feeding it from the load side of the GFCI. This idea comes from the fact that the state rental inspectors come with magnets to test that the plate screws on that switch are plastic not metal, with the idea that somehow that metal screw can get energized. So while everything is open, it occurs to me I can feed the ceiling light from that GFCI also instead of the general circuit it's now on. Our reading of code says that as long as the 20A line is only to that one bathroom we can feed the outlet & lights from it.
Searching has led me nowhere on this one, answers are all over the place including "good idea" "there's no way for a switch to get energized" and "it's against code because all the lights in the bath will go out in a fault".
Is this unnecessary caution, dumb, smart, illegal, or what?