Maybe you just want to keep them on edge, maybe you want to make sure they're paying attention, maybe there hasn't been a roll in a while and you just wanted filler.

How have you made players roll when they didn't actually need to?

Every now and again, a perception roll with no actual DC and just going "Hmm, interesting", makes me chuckle a bit.

I couldn't decide which character to make the villain focus on and have a scene with, so I had them to pick a number between 1 and 10 and told them they didn't want to be closest to the number I was thinking of outside of the game. Instant panic.

I love a perception roll to see how much they notice about a room. Also when players were walking through a dangerous town I had them roll perception with no context - if they rolled badly, later they would find they had been robbed

The classic.

I once had a player roll deception checks for believing their own bullshit.

Character (and player, too, admittedly) was a notorious narcissist hypocrite who would lie to people constantly about shit, even stuff that didn't matter. Just a compulsive bold-faced liar that would play things off as "just joking" whenever she got caught, so, since I felt like fucking with her for always being an annoying shit, and given I had spent 7 years studying communication theory and psychology, I knew that eventually compulsive liars begin to believe their own fabrications, effectively gaslighting themselves into a completely imagined reality. This is especially accelerated by personality disorders, so she started to develop traits from the long and short term insanity table as character flaws.

All very much unnecessary but it resulted in the character being revealed as a lying piece of shit over a period which was fun because they used Deception as a crutch in every single encounter with anyone ever, hoping it would magically get them whatever they wanted. Kind of like a player who thinks a +25 to persuasion means you can just march into the king's hall and demand he relinquish his kingdom but with fucking with people and lying about everything.

rolling investigation in a room i have alrady told them is completly empty is a recurring one for some reason. lately i just make up some coin in a hidden nook so they stop looking.

It's a classic until they roll a 20 and you either have to come up with something really quick, or give up and say they notice nothing

Yes. Because the ranger felt fucking useless, I made him roll a lot during exploration to feel important and had contributed something to the party aside from being truly fucking useless in combat. Really, how fucking useless can a ranger be?

Sometimes if they're getting lippy I'll have someone roll a d20, make any noise in acknowledgement, and refuse to ever discuss.

There was never any reason.

I love the random “I need everyone to make a wisdom saving throw” out of nowhere, then whoever rolls lowest, ask to look at their character sheet, nod, and continue on with the game

You kidding? That makes it even funnier

A few sessions ago the party was investigating a warehouse that was a front for a criminal gang. While searching they found a hidden door leading to a basement. They spent like 10 real life minutes talking about who would go first, where or what traps were there and so on. I had planned exactly zero traps on this door. So when they finally open, naturally I have the front man roll a dex saving throw. He gets a natural 20, so I describe I great detail how he acts with a reaction speed beyond anything he’s ever accomplished before, gracefully and artfully dodging out of the way of… nothing. Got a lot of laughs.

Had a fight in a dining room with a long table down the middle. A player wanted to jump over it, so I asked them to roll acrobatics. (Just to see how well they land, but I didn't tell them that.)

"What did they steal?" 'the wizard' "I thought Clara was being kinda quiet"