The AKC states that their shows are for the purpose of evaluating breeding stock (similar to showing cattle and horses at 4H or the county fair). The field (hunting), tracking, earth dog and obedience classes were originally developed to evaluate a dog's ability to do what it was bred to do, giving the dog further breeding credentials.
For many years, spayed or neutered purebreds have been allowed to compete in many performance events. Allowing mixed breeds in was the next logical step. The UKC has allowed it for years. There was resistance in the AKC, and I understand that. No one wants to be seen endorsing random dog breeding, and by allowing mixes you could claim that this leans in that direction. But it's a stretch.
I sense a little "keep your grubby mixed breeds away from my classy purebreds" attitude here, but this is at least a step in the right direction.
Mixed-breed classes can be held at all-breed sanctioned/licensed/member stand-alone AKC Companion Events. The definition of a stand-alone AKC Companion Event is an AKC Agility, Obedience or Rally event that is NOT held on the same date AND show site as an AKC All-Breed dog show, Group Show or Independent Specialty. Mixed-breed dogs compete in separate classes from purebreds.
The significant benefit to the AKC is a new source of income. For a $35 fee, a mixed breed dog gets an AKC Partners registration number, a subscription to AKC Family Dog magazine, and lifetime enrollment in the AKC Companion Animal Recovery Program, all very nice benefits to the pet owner. And the AKC builds their marketing database significantly, without "endorsing" mixed breeds, or worse, "hybrids." Think of all the designer breeds that can now compete: labradoodles and goldendoodles will at last have a place to showcase their talents. (I can see the conformation crowd cringing.)