I've had some strange experiences that I think of as "Schrodinger's Mechanic" type play. The game has rules for resolving something, those rules are used sometimes, unless the GM has decided not to use them. There's shades of this in conventional rulesets, "don't roll if the results don't matter" kind of leans that way, but I've been in games where instead we'd go from using standard skill checks to climb things, to suddenly interacting with a bespoke climbing system for a specific cliff that didn't involve using skill checks at all (it was a push your luck dicepool thing) and back again.