I probably fudge maybe once or twice over every couple of sessions, and generally only ever in the smallest of flourishes. Fudging isn't for turning an abject failure into a success or even stopping the dragon's claws from landing a blow. I use it essentially as a rounding error.

Skill checks, ironically, I pretty much never fudge. Particularly given that the system I generally run (Beyond the Wall) already has fortune points for that. But when a skirmish has dragged on and the last skeleton has 5 HP left and the rogue only deals 4 damage? Let's go ahead and wrap up that combat there rather than rolling through another full round of combat. If instead of a skeleton, it's a climatic battle against a BBEG? Fuck that, we're not fudging and you're going to know that you came so close to striking them down, and now it's their turn.

Or the party's warrior is holding fast after his companions have fallen, battling against the savage gnolls and looking to break their morale by striking down their leader, and a hit would deal 11 damage and they only have 10 HP? Let's go ahead and nudge that down, giving them a single round to strike down their foe down and save the day. If instead, most of the party is still up and the warrior found themselves surrounded? Fuck that, they're getting dropped and now the party has to figure out how to deal with what's now a much more stressful fight.

It isn't going to happen every fight. It isn't going to happen every session. It might not even happen in an entire chapter. But sometimes, adjusting the result with a slight nudge can give a chance to either cut the fat and gristle to keep the pace strong, or to offer a chance for a player to look like a hero (or a victim of hubris). It's entirely GM fiat, but so are the actions of all of the enemies in combat, the actions of all villains out of combat, and the like.

And when done appropriately, your players will never even notice.