The real issue is whether it is artful or artless GMing. Does fudging lead to a better play experience for everyone, or does it lead to a worse?
Not very often. When the GM makes something hard or impossible by fudge the players will rarely feel great about it. Having the GM save their favorite NPC from a player trap with fudging does not make the players experience better...even with the GM saying "oh wait guys I got a super awesome combat encounter with this NPC planned later".
BUT. It's also true the other way where the GM runs a 'safety game' so that by fudging, nothing to bad, or troublesome or inconvenient happens to the characters so the GM can lead them right to the "fun parts" of the game. This does not make for a better player experience either.
Maybe worse is the GM that jumps around. In the first hour all the poison darts miss, even when the foes roll 20s or totals of like 30, as the GM is quick with a fudge like "oh they have a -11 to ranged attacks...hehe". But then just an hour later the DM is like "oh two 20s are auto hits so both characters get hit with poison darts.".
This is why I go with the firm: Let the Dice Roll where they May!
I find the best game is where everyone knows and accepts the random dice rolls. Yes, some times it leads to a TPK an hour into the game play where some kobolds obliterate characters with some amazingly high rolls. But you just accept that in move on. Though it's not that often such an extreme.
Just last weekend, a group had the plan of sneaking into the Dark Tower and destroying the Orb of Destruction before the bad guy could use it. They planned and equip up ahead of time, then did the stealth entry. They had to get past tons of traps, guards and protections. All quietly. Each bit of the way, a bad roll could have sounded the alarm. Though these were good players so they avoided having to roll to do things as much as they could(like they had a stolen ward token for the Orb Chamber so they did not have to deal with the protections there). They made it all through the tower...and there was some huge tension where they were almost caught by a low roll of the dice. But what made it so tense, is that it was real. Just a couple numbers lower and they would have been trapped in the tower surrounded by foes. Everyone knows the rolls were real: whatever rolls is what happens. The players were ready for "plan B of fight out way to the Orb room", but sure did not want to do that. And right at the near end there were some very close calls. But the PCs made it, and destroyed the orb and escaped. And every player knows for 100% sure that I made a very hard complicated adventure and I was more then ready and willing to have things go any way possible, but I did nothing the "fudge" any outcome.