I'm sorry, I am missing your point "if you are wet sanding there should be no problem with residue anywhere." Isn't that exactly when you DO have residue, when you are wet sanding? Now, if you have JUST a body doing a complete restoration where the body is painted and then you assemble it, I can see that you could use a lot of water and rinse it off and that sort of thing where you have no residue, is that what you mean? Me personally, I always have some residue to clean up in the jambs and, inner fenders, if the body parts are assembled on the car.
But this is all personal preference for each of us as we all do it a little different. Certainly no right or wrong in masking or unmasking or wet sanding or orbital sanding, just personal preference that's all. If we toss out these ideas of our personal preferences someone doing it for the first time or once in a while can pick up some different ideas on how THEY may want to do it.