I don’t always run a timer, but it is a tool in my box.

Mostly it comes out when I feel like the players are spinning their wheels. Like, they know they need to get into the server room on the 10th floor. There’s a front door with security, a back door with an alarm, etc. The players are just going round and round with ideas but not doing anything.

I’ll say “I’m starting a five minute timer. If it hits zero, something interesting will happen”.

If it hits zero and they’re still stuck, then as foretold something interesting happens. A rival group rolls up and firebombs the entrance before heading inside. A security drone spots them and is calling the cops. Whatever. Something that forces them to act.

In combat rounds I sometimes do the same, but only if it feels like they’re not making progress. Maybe it’s a little rude sometimes, but I value keeping the scene moving forward. I don’t want to keep spending three minutes on “should I move? How far can I move again? Is there a range penalty? What if I use a spell first can I still shoot?” stuff. Especially if it’s rules minutia they should already know.

The amount of times I had to remind an old group’s bard that yes, in DND 5e you can move AND take an action was too high.