A laser only coincides with the point of impact at two points on a bullet's trajectory (ETA--at most). If hitting close to what you're aiming for is OK, then I guess that's OK, but if you're shooting for accuracy, that won't help you.
That said, it can be helpful as a training tool. Set up a GoPro to video the target, turn on the laser, squeeze off a few rounds, then review the video to see how well you're doing in keeping your point of aim as you fire the weapon. If you're doing something consistently wrong, you should be able to see it pretty clearly as you watch the dot move around.
Also, they do look cool. I have one lying around somewhere. I took it off because it wasn't useful, but when I first got it I spent several nights putting the dot on things as far away as possible. It was neat.