But hey, come closer, a little closer. I don't want my players to hear. It's a secret. I do fudge the hit points or modifiers at times. Sometimes I do it in the player's favor, sometimes in the monsters favor. Depends on how I want the combat to go. I think it's the better way to do things. Fudging rolls makes players really paranoid. Fudge the modifiers or hit points or numbers, they never know better. Much wiser than fudging rolls.
this touches on another aspect of the fudging issue.
playing with the dice rolls in public view and vowing to never fudge sort of assumes the system is so perfect and balanced (and run correctly by the GM), that all encounters are "fair". I quoted that word and use it loosely for a reason.
In the realm of not changing die results, but changing HP on a BBEG, how is that different than the work you did during adventure design, where you decided the BBEG would have 200 instead of 100 HP?
What rules guided you that said 200 HP is fair for the NPC to have when you designed the encounter?
If you can build unreasonable or unfair during the design stage legally, what makes changing things during the execution stage illegal? Functionally, the outcome is equivalent.
Personally, if I have decent challenge level calculations that I follow during the design stage, I then can assume that my BBEG is of a correct difficulty level over the party, and that whatever happens from the dice rolls should be accepted as fair.
I don't know about 4e, but prior editions have yet to hit that mark. As such, I think that drives some GMs to make in-game corrections when they are realized.
When I fugde, it is generally to save the life of a PC that would otherwise die so quickly that the player cannot make a course correction. Frex, round 1, the BBEG hitting the PC for enough damage to kill him. The PC would have no chance to realize he is in over his head and withdraw. Whacking him down to 2HP makes it pretty clear that his next action should be to change tactics, or he will die. You can bet, the next round will kill the PC if I score a hit and the PC was dumb enough to stick around.
I never give the bad guy more or less hitpoints. I never negate a saving throw to spare the bad guy. I might be a softy for giving the PCs a second chance from damage, but that's about as far as I go.