It pretty much is just set...a keypress is a static command/press without pressure sensitivity, whereas mouse-turning is as fast, or as slow, as you drag your mouse. You can still mouse turn on your main without breakin lowbie follow and the "cone/range" for casting is pretty wide(If you start casting and a target ends up just off to your right and ahead slightly they'll still be within the "Must be in front of you" range/cone); I mouse turn my main and tap strafe if I need to turn the alts but usually the target's still within the "frontal cone" range to cast at lol