@JeremyECrawford I'd love to hear the background on why 1s and 20s aren't auto-success/fail for ability checks. Would you be willing to share?
— Callum Grier (@CalGrier) April 10, 2018
In the realm of ability checks, there are meant to be tasks that only an expert can accomplish and other tasks that an expert would never reasonably fail. For such checks, we don't give a 1 or 20 on the d20 any special meaning because we don't want to subvert that intent. #DnD https://t.co/no59E2F2XA
— Jeremy Crawford (@JeremyECrawford) April 10, 2018
They basically are: if you can’t fail even on a natural one, or succeed even on a natural 20, there’s no point in rolling the die at all, you succeed/fail automatically.
I went with that philosophy until I realized I couldn’t keep everyone’s bonuses for everything in my head.
So yeah, I’ve occasionally asked for rolls when they couldn’t succeed and when they couldn’t fail.
They also come up in contested checks and group checks, but that’s another story.
Player: I try to pick the lock.
DM (knowing the DC is 25, and the PC only has a +3 to their roll.) No, sorry, you can’t.
Player: You’re not even gonna let me roll??!?
Other players: Oh wait, we know Steve COULD roll with a +5, so now we know the DC!
Saying “there’s no point in rolling” takes away player agency, and encourages metagaming. Always let the player roll.
My position is somewhere in between. I don’t quite agree with those that say don’t bother to roll if the player can’t succeed, for the reasons you give, but there are cases where you DO want to make it clear that the attempt is not even worth attempting for any PC or mortal creature. E.g. if someone asks to jump to the moon, I’m not going to let them roll an Athletics check. (An extreme example, to be sure, but I think it illustrates the point. ALWAYS allowing a roll encourages cheese and slows down play pointlessly.)