Depends on the game. There really shouldn't be a reason to absolutely require one aside from odd circumstances.

Ask in the game specific forums to make sure.

In general you can time a run using your video instead of a live timer. That's usually more accurate anyway.

"There really shouldn't be a reason to absolutely require one aside from odd circumstances. " - Pretty accurate

The only particularly compelling reason I can think of is for autosplitters.

Thats why WSplit > Livesplit ;)

Llanfair OSsloth

Chronograph Metal Digital Sports Timer Stopwatch

Requiring a timer to submit is like saying that a speedrun isn't a speedrun unless it is timed, which is wrong. A timer should never be required nor be used as proof.

I never even use a runner's timer when I retime a run. Any moderator who wants to see a timer doesn't know what he's doing.