I almost never set a timer on my watch by hand. The main reason is that I like to give my timers names. And the only way to do that on the watch is via Siri. So I’ll raise the watch and say “Hey Siri, 5 minutes” if I want an unnamed timer, or—more frequently— “Hey Siri set a 5 minute tea timer”, or “Hey Siri, set a 15 minute pizza timer.”