They're useful in a small number of situations. A crutch in most others. I typically train for simplicity. That is, I try not to train for using different techniques/equipment for different situations, when one technique/piece of equipment will work for those multiple situations.
For example, some people teach Tap, Rack, for a level one malfunction (failure to fire), teach the Rack and Roll for a level two malfunction (stovepipe), and Rip, Rack, Rack, Reload for a double feed. When I train malfunctions, I train that when my gun goes click instead of bang, to Tap, Rack and Roll since that will clear both Level 1 and Level 2 malfunctions. It's a bit slower, but I don't have to think about the type of malfunction, I just work off instinct.
Same goes for lasers. I don't feel like training on a sight system that will only work for me in a small number of situations. I'd rather train to use the iron (night) sights for all situations. That way, when I am in one of the fairly uncommon situations where a laser might be better, I don't have to think about using a different system. I already know what I'm going to use instinctively.
Having said that, I've seen good arguments for people using them because their eyesight is bad (though, if it's bad enough, I'd slap a reflex on there instead since it'll work in bright light also). In the end, use what works for you.