Benefits of mouthguards:

The benefits of sports mouthguard protection has been well documented. A 1995 study by Dr. Raymond Flanders on the high incidence of oral injuries showed that in football, where mouthguards are mandatory, only 0.07% of all injuries involved teeth and the oral cavity. Conversely, in basketball where mouthguards are not worn, 34% of all injuries to players involved teeth and/or the oral cavity!
Obviously dental injuries could also be significantly reduced if children, teenagers and adults involved in the following sports wore custom fabricated mouthguards: soccer, volleyball, baseball, softball, rollerblading, skateboarding, martial arts, boxing, hockey, kickboxing, rugby, lacrosse, and mountain biking, to name some.

Mouthguards help prevent
Concussions:

Concussion is an alteration
of consciousness, disturbance in vision and equilibrium caused by a direct blow to the head, rapid acceleration and/or deceleration of the head, or direct blow to the base of the skull from a vertical impact to the chin.