Klash I think what you may be talking about is: Aileron (to) elevator mix and sometimes referred to as Tailerons. In the full scale world it is most seen on military aircraft and very few civil aircraft.

As you suspected the idea is to increase the roll rate by mixing in an aileron function on the split elevator halves of a conventional configured aircraft.

I,am sure it has been used on RC aircraft but suspect that for most of us there is very little if any advantage.

John