I am a proponent of laser sights.
As stated above, it allows you to put your front sight on the target itself.
I have read the statement about defensive shooting: "If you have a good shooting stance, you are not moving enough and not using cover effectively".
Any time you cannot have a good two handed stance, the laser will give you a tremendous advantage. Shooting around a barrier...like a doorway or corner in your home...it will allow you to get on target without bringing the weapon to eye level. It provides the same advantage from any non-standard shooting position: prone, on your back, across your body, turned looking over your shoulder behind you.
True, they do use batteries which can fail but you are no worse off with a failed laser than you would be with no laser and if you maintain them, they should be ready when you need them.
You still need to practice standard shooting techniques without the laser to maintain your trigger control skills and body indexing, but you will find adding the laser to your training session will be a big assist.
Your first impression will be that using a laser makes you a crumby shot. That dot will be jiggling all over the place. Of course it has not made your hold go to crap, it simply is showing you the facts...movement that you could not perceive with your normal sight picture. I do believe you could take an accurate pulse by watching the movement of the laser dot on target....
Dry practice with the laser is embarrassingly revealing but allows you to work on better control.
Sight your laser so it's point of impact is the same as the one you choose for your normal sight allignment. Some laser sights are not adjustable (LaserMax internal laser in a Glock, for example) but they are accurate enough for defense work as is.
Ideally, you would want a switch that would automatically turn on the laser when your trigger finger contacts the trigger, but I don't think that will be practically available. I do think there is a model that senses the finger inside the trigger guard to turn it on and off. You don't want it on until you are on target and your finger is on the trigger so a switch near or under your trigger finger extended before placement on the trigger would be good. I avoid any off hand switch to turn the laser on because I don't thing a two handed grip is likely in a defense scenario.
In any situation where "point shooting" is called for, the laser makes it as close to fast aimed fire as you will get.
I used to practice "fast draw" with a Ruger Blackhawk with wax bullets in special cases using a powerful primer for propellant and a shirt on a coat hanger for "hip shots". You could see where the wax bullets hit to check accuracy. With the laser, you can see where it is when the shot would have gone off.
I have an internal LaserMAX installed in my Glock 21 and 23 and intend to install one in my 21SF.
I am putting together a tactical 870 and intend to install a laser sight on it, a Viridian is under consideration. Their green laser is easier to spot in all light conditions, particularly brighter light, compared to a red laser and they have models with a laser and a strobing light. (they have a green laser and light combo that will mount on a pistol rail, but I prefer not to have a light mounted on a handgun).
Take care.