Laser sights offer shooters a different, and often faster, way to aim that doesn't require them to line up iron sights or focus on a crosshair. When properly zeroed in, a red dot allows you to fire from nearly any position such as from the hip and hit where the laser is pointing. This works best in close quarters situations and becomes less effective for long range shots.
Tactical flashlights allow players to light up dark rooms or see better at night. Higher lumen flashlights can also be used to flash an opponent and temporarily or partially blind them by interrupting their night vision. Tactical lights are rail mountable and can also be used in a handheld mode. Some have a strobe function which allows them to be used as distraction devices.
Many lasers and tactical lights have a pressure activated switch which makes it very easy to toggle them on and off. The switch can be attached to a gun's foregrip or pistol grip.