Well say you have nature 6, and you’ve been using it pretty heavily so it’s taxed down to 2. You’ve got 5 success and 4 fails, then if you want to get really any benefit from it in the middle of said Weasel dungeon, you’re probably going to want to take that -1 and go back to your new full Nature 5. And if you’ve been using your Nature this much, but don’t want to become completely mouse-like it’s going to be as good a time as any to knock back down to 5.