You might tear things up in the drivetrain if you run the locked rear on high traction surfaces.Will probably experience some understeer(front end not turning as well).You may have the rear end slide around more on very low traction surfaces.The steel forward only should help the strenghth.I have not tried a locked diff yet myself ,this is just what I know from 1/1 scale vehicles.
It will offer maxium power equally to both rear wheels.Best suited for low traction ,straight line use like tractor pulling,sand drags, mud bogging,or even rock crawling.
My 2 cents