the Jester
Legend
Really? Then why let the rogue roll the dice in the first place?
Usually in a case like this, the DM rolls.
What is the function of the rogue in a group if not be sure there is no trap (or be sure there is one) with a "critical" success?
I'm sorry, but I'm having a hard time taking this seriously. Are you suggesting that there is nothing that makes a rogue a valuable contributor to the party if he doesn't roll a natural 20 while searching for traps? Because I can think of tons of other functions for the rogue. Scouting ahead, sneaking away, trailing a mark, opening locks, skills in general (thanks to Expertise!), etc. In combat, you've got sneak attack.
Seriously, I have rogues in my campaign who have never checked for a trap, yet they seem quite functional and useful.
What exactly is that "something" that is lost?
Improved immersion. However good your pcs are at playing down what they know vs. what their characters know, it does make a difference, at least for every group I have ever been in. For example, if I play through a module that I've read, even if I consciously avoid acting on that knowledge, then I simply know too much about what is going to happen to enjoy that module as fully as if there were surprises in it.
That a DM cannot play a dirty move on the players even though they rolled high?
That's kind of out of line. The idea is not that the DM wants to "play a dirty move on the players even though they rolled high", it's that the players should not know how successful they were. Look at searching for a secret door- "I search for secret doors. Oh, I rolled a 7. I'll try again.".... vs.... "I search for secret doors." "You don't find any." It's not some big mean DM conspiracy to take advantage of anyone. It's improving immersion.
That his or her precious trap will not work?
Yeah, again, I think you're reading in here. I haven't read every post in the thread, but I think the general attitude of DMs who don't let the pcs know what they roll every time is more "You don't know the result" than "Yay, I can cheat!!"
Which brings us to...
We all have to live with the result of the dice rolls, don't we?
Absolutely not- if you're the DM. Fudging is a time-honored tradition. Not every DM does it, but almost every DM does it once in a while. And in my experience, it's almost always in a way that favors the pcs. Personally, I really avoid it; I don't think I have fudged since around last Christmas (and this is averaging 2 to 3 sessions per week since 5e launched), and I almost always roll in the open. Nonetheless, I roll things where the pcs shouldn't know the dice result out of sight, including many Perception and Insight checks and some other things.
If a player 'fudges', on the other hand, it's straight up cheating. There's a different standard because they are in a different role.