Benefits include better health.
They are less suseptable to genetic disorders because they have a wider genetic pool. Genetic disorders are caused by inbreeding family members, sometimes necessary to "improve" the standard of the breed. That is not the case with mix breeds.
They are more steady. Inbreeding also causes nervousness and insanity. Also, dogs like terriers have been bred to kill small animals, so sometimes you get a pet that won't tollerate other pets. Or, collies and shepards that herd. They are bred for high herding drive and you get a pet that herds guests, neighbors, kids, rocks, buckets, anything. Constantly. And you have to overcome that with lots of training. In a mixed breed dog, that can be diluted down so it is not a problem.
It is also fun to guess what breeds he is made up from. Once you decide, you will find others who disagree with you and it can be a real conversation starter.
I'm a big fan of Mutts, can you tell? :)