One of the actions that Activator lets you assign to a gesture is Do Nothing (override default behavior.) But for some reason, a few versions back, Ryan Petrich decided to make it so you can only assign Do Nothing to certain gestures.
Notably, he made it so you cannot assign Do Nothing to swipe-in-from-top-corner gestures. I used to use those as part of my efforts to prevent the NC from ever appearing, before some tweaks came out to totally disable the NC altogether.
So, nowadays I do not really have a need to assign Do Nothing to any gesture, but I still like having the option to do it if I want toI strongly dislike being artificially prevented from assigning an action to a gesture, whether or not assigning that gesture will actually do anything.