Leave 'em on all the time in the circuit. I was flying last night, a bit murky, 3 in the circuit plus me. 2 had strobes, one didn't. Never saw the one that didn't until he was on the runway as I was downwind. Strobes are great - landing lights are only visible when someone is pointing straight at you, useless when converging.
To the list of useless things (runway behind you, fuel in the bowser etc) add "lights that are switched off"
You might also add "Chocks Wahay in the left hand seat", but that's another matter!