You will find people that love them and some that hate them.
All accessories are supposed to increase your effectiveness with your firearm, whether it be lasers, lights, grips, optics, etc. If you find lasers don't help you, don't use them, if they do help, use them.
No accessory should replace the basic fundamentals of shooting, unless your physically incapable of performing those fundamentals (ie poor sight, disfigurement, positioning, etc)
Pros (with training): Sight acquirement if unable to use irons. Faster acquisition. Some deterrent value. Gives you more options.
Cons: Runs on batteries. Another part that can break and to maintain. Can take away from practicing with irons, whether it be laziness or time constraints.
Do I use one? I have a laser light combo on my shotgun, no rail on my primary handgun otherwise I would have one on there too, for the pros above. I make time to reduce the cons as much as possible (maintenance and failure drills).