Horses have been improved by cross breeding for centuries.
The Missouri Fox Trotter was created from a blend of American Saddlebred, Standardbreds, and Tennessee Walkers with the Morgan, Thoroughbred and Arabian.
The Quarter Horse was also created from a mix of breeds, including Thoroughbred, Mustang, Arabian, and Morgan.
The Warlander is a cross between a Friesian and a Andalusian.
What are, in your opinions, some advantages and disadvantages of crosses today? (Mules included)
I had the chance to meet personally a young Missouri Fox Trotter x Arabian filly. I knew the stud but unfortunately was unable to meet the mother, as she abandoned the foal and the filly had to be hand raised. I assume she was not as light as some, more of an average sized Arabian, not to sleek but not to bulky.
An advantage would be, I suppose, the added muscle from the Foxtrotter. Perhaps expanding her discipline possibility's. Another advantage of the cross, could also be the more refine Arabian-type head, and slightly sleeker frame.
A disadvantage that I could see occurring would be a confusion of gaits, even resulting in a more uncomfortable ride.