Use of the revolver in mounted combat might have been a bit different than some of us might have always thought. For instance, Mosby always used small bodies of mounted men for limited hit-and-run missions. I can't think of an instance in which Mosby decided to take on mounted unit of any size and allow the result of combat to be decided on horseback.
A revolver could be used enhance the impact of surprise, to create confusion and disorder among the defenders. It wasn't as useful for inflicting casualties as a saber, but might be a great deal better for noisy 'shock-and-awe' attacks on wagon trains, isolated posts or poorly-guarded camps. Those who didn't run could quickly be pursuaded to surrender. In most cases, that may have suited Mosby's purposes better than simply placing enemy soldiers out of combat.