I've owned & shot a few handguns with laser aimers(CT Lasergrips). They have limited practical uses on a concealment/duty sidearm but are NOT a replacement for marksmanship or skill training.
I owned a M&P 9x19mm full size in 2011/early 2012. I'd made plans to carry it as a armed security sidearm. I considered buying a X5 mag extender(more 9mm rounds) & a Viridin green X5L type laser & white light.
A set-up like that would add weight but lower pistol recoil & offer a possible deterrent to a lethal force event. Bad guys don't like being shot.
Savvy(ie career crooks) felons also avoid the armed cops or guards who are well armed or can use tactical equipment(See Ben Affleck's The Town
Crimson Trace & Lasermax often promote their systems to armed citizens & sworn LE agencies by saying how the use of lasers(laser aiming systems) help deter violent crimes. This is true but don't rely on it 100%.
R&D by the US military has also shown that the human eye is drawn to movement. Aiming a bright green laser dot & firing a well aimed shot can help reduce the risk to bystanders or to the armed citizen.