It is remarkable how much more you can accomplish if you have a proper mentor to guide you. This is true not only in daily life, but in the realm of magic as well. A true master of magic, equipped with proper means of delivering her message to her disciples, is often an invaluable asset to any group of magic-users. Indeed, the benefit of having a proper mentor is very often mutual as the teaching party must exert herself to clarity her understanding of things to pass it on.

Or as Seneca put it in his undying words:
"Homines, dum docent, discunt" - "Men learn while they teach."

A target can benefit from several sources of enlightenment at once, but there is a limit of how much guidance one can really receive.