Maybe I'm just lazy, but I think timers are the best thing to happen to aquarium lighting since electricity. I wouldn't have a tank without one. And the fish seem to appreciate the consistant day/night cycle.
Agreed, I bought two $5 mechanical timers from Target. Some of the best money I've ever spent on my aquariums. No more forgetting to turn the light on or turn it off at the right time, it automatically comes on and turns off just when I want it to. Even works when I'm not home. I'd say everyone should get a timer for their lights.
inless your tank had access to direct sunlight (which would cause you all other sorts of problems), you will want to have the light on at some point. not all fish like to live in alaska. a timer is a cheap and simple solution to your lighting quandry