For the lucky riders who don't need to ride in the rain, fitting mudguards is far from necessary. For the rest of us, adding some protection from mud and spray can make a huge difference to riding in the wet.
While a lot of the guards on this list seem very minimal they actually do an impressive job of protecting the most important area: your face. Riding in the wet becomes far easier if you don't have half the trail spraying all over your face. Even if you are wearing the best mountain bike goggles, having a mudguard should keep your goggles fresh and vision clear to the bottom of the trail.