Target Acquisition
The greatest advantage of using a laser sight on your handgun is quick target acquisition. Most laser sights activate as soon as you apply pressure to the grip, sending a beam directly to the projected point- of-impact of your pistol's bullet. Using the laser beam gives you a greater view of your target, since using the conventional open sights on your pistol obscures the bottom half of your target.
Intimidation Factor
The intimidation factor of a laser sight comes into play when you are using a pistol for personal protection. If would-be aggressors can see the point of a laser beam striking their bodies, the psychological aspect of knowing that the beam represents exactly where the bullet will strike can often cause them to reconsider further aggressive action.
Daylight Use
The greatest disadvantage to using a laser sight is that the laser beam can become difficult, in not impossible, to see in brightly lit conditions, such as daylight. While green laser beams perform better in bright light, red lasers (which are more commonly used) are easy to lose sight of in high ambient light.
Position Giveaway
If you're attempting to conceal your position, particularly in a tactical situation, a laser beam will quickly betray your location. Ironically, the same feature which makes the laser beam intimidating is also its shortcoming; since the intensity of the laser beam is just as bright at its origin, you will be easy to spot.