In life or death situations, I tell my players what they need to roll to succeed.
Oddly enough, I don't fudge my players' dice either. I don't know exactly why it would be a relevant example.
Plus there's no changing a 1 or a 20. If that powerful foe confirms his crit on one of the players with his smite attack, you know the players are in for a world of hurt (and it might spell the end of one of the pc's). And if that BBEG rolls miserably on his save, no bonus in the world is going to save him from a miserable defeat.
Whereas if the dice have been giving my players a bad run or seem excessive to the pacing of the game, I'm quite content to knock a crit I land on them down to a regular hit. Or I've dropped a die off the finally tally, or the strength modifier. In a PF1 game, the halfling rogue tried to tumble past a triceratops skeleton. Seemed a perfectly reasonable thing to do - but (in one of the biggest mistakes of the PF revision of 3.5 rules) tumbling past big things is
really (pointlessly) effing hard in PF1 and she took an AoO - I rolled a threat, confirmed. The 4d10+30 was, quite frankly, a bit excessive so I chose not to double the strength bonus from the crit which shaved 15 points off the total. It had the appropriate effect of putting the fear of death into the character (as played by the player since she was now in single hit points) but didn't kill her.
I don't have to let the dice be their full arbitrary selves to have varied and interesting results.
I remember a session where a druid-pc had to stop a ghost ship from ramming his ship with his love interest tied to the bow. He summoned a water elemental, but the ghost ship opened fire on the elemental, quickly reducing its hitpoints. I straight up told him that he had 1 more round before the ghost ship would collide with their ship. The water elemental was able to reach his love interest, but the cannons managed to reduce the water elemental's hp to exactly 1, which was just enough to save his love interest before the ghost ship smashed into them. Ever since that event, I let the dice fall where they may, because you never know what might happen. It is great when these things are out of the DM's hands.
And if the dice had dictated that the water elemental die rather than eke through with 1 hit point and save the love interest? I doubt the outcome would have felt as great - maybe even a little bitter since the player's desperate (but actually pretty good) plan failed because of the fickle dice.
In a later session of the same campaign as the example above, the PCs had a chance to scry on one of their opponents. It failed - he made his save. So they hatched a plan to get some more personal info and items to undermine his ability to resist the spell. When the saving throw came up again, I ignored the roll and decided he failed. I didn't want the dice to ruin the really good plan the players put together. Rebuffing them so they try another approach is worthwhile - doing it again when they're being clever and careful just because a roll is involved? Not doing it.
Letting go of the outcome of dice may sound scary to some DM's. What if a campaign that has lasted for years, suddenly ends with a crit from a monster that outright kills a player-character? Not during some climactic boss battle, but during a simple encounter? It happens. And yes, that is always a shocking and sad moment, to lose a player character that has been around for so long. But it is also what makes playing D&D so exciting. I've seen this exact scenario happen, but you know what? The player in question was okay with it. He even appreciated the fact that the rest of the group was so upset about it; that they liked his character so much. They asked if they could redcon the session, but the player refused. My character is dead, he said, and to undo that would ruin the journey and the point of the game.
That player isn't everybody who plays. Not everybody is interested in that kind of game - hence save game on computers, magic capable of raising the dead, Hero/Force/Destiny points used to save a PC's bacon, etc. I actually suspect they're in the minority these days given the number of ways people have of ameliorating deadly outcomes even strictly rolling the dice.
But boy do the debates on the topic seem to devolve into claims that those of us who do edit the roll results are missing out on some level of fun or purity of the game or just playing on "easy mode".