in general I agree with you Diane,but with a reservation ,to some extent actually doing it is part of the learning process,particularly performing ,practice at home is necessary ,as is preparing for performing[alexander technique ].
but so much can be learned when on stage,there is nothing to beat learning how to perform by actually having a go,it is similar to acting in this respect.
of course it is necessary to know ones lines or the song,but interpretation ,is often spontanteous ,and stage craft can be learned on the hoof,that is about interacting with people,and there is no better way to interact than in the flesh.