Tired of breaking those shitty dual filament bulbs on your rigid chop? Try an LED tail light! Not only are they brighter than a filament bulb, they draw a fraction of the voltage! Easier on your bike's charging system!
A tail light is important so people don't slam into you when you are slowing down! Granted, a tail light doesn't remove the stupidity from the drivers around you, but it lets them know you plan on not going the same speed and may come to a complete stop. Basically, its cool to not die by being rear-ended while on your bike.