Let's say Hero has either "nuts" or air, and Villain has a bluff-catcher, but also some slow-plays. If Villain is OOP, I have a theory that he only leads his traps if Hero prefers to check back his entire range if Villain checks his traps.

By leading, Villain never gets a bet out of Hero's air. Some of Hero's "nut" hands will also fold to keep Villain's bluff-catchers indifferent between betting and checking, so Villain will also lose a bet from some of Hero's "nut" hands. I also believe that Hero will call a jam more often after betting because his pot odds will be better.

So leading always seems worse than checking, unless Hero is not betting in the first place.