I did fudge a bit in my last session and give an NPC an extra healing potion in order to keep one of the PCs alive.
I just don't want to kill off a heavily invested in character for no other reason than the dice said so.
Ergo, there isn't much I won't do to stop a PC getting pointlessly killed.
I know our DM fudges on occasion. Last week, I happened to be standing at the instant he rolled damage for the two zombies hitting the barbarian (who was down to about three hit points)... so I saw the pair of 8s hit the table. The DM declared five damage, and the barbarian went down unconscious.
I'll cheat if the players are getting an incredibly bad (or sometimes good) run of luck. Basically, if through no fault of their own, they're getting hammered (They keep rollings 1s, I roll three crits in a row), are adjusting their plans to account for that, and are still getting beat up, I'll give them a break. Likewise, if an important enemy is about to get killed in the first round because three players crit on him after he loses initiative, I might fudge a number or two.
Very rarely, and only to save a player character from abnormal luck or for the good of the story.
I admit I have turned a lethal situation into something else for a random encounter or something not critical to the campaign story.