I've spent today arranging rehearsal space and a common schedule for an improv troupe. My current class will be playing on stage tomorrow night as well. I do perform, if very irregularly, a parlor-sized act in the real world. So, I hope to weigh the pros and cons of improv from the middle ground.
First of all, John Rhys-Davies was speaking entirely about different schools of acting and/or theater. It's almost certain that he meant this form of
Improv. There are other schools of acting which tend to abhor improvisation. That happens.
As a form of acting, Improv also teaches the kind of tools that
Andrew Garfield used to land the Spider-Man role. Bill Murray has made a lot of wonderful movies through improvisation and ad-libbing. Not all of his roles were comedic ones.
There are a lot of schools of acting. John Rhys-Davies has his preferences and has been successful with his own career. Other people have succeeded by coming from other schools of theater. That happens in any craft, including magic.
With that out of the way, I'm ready to talk about magic.
If I am doing something that requires the spectators to merely spectate, then I need a script and, typically, some form of choreography.
I even write my own music for magic acts. My club has had invaluable advice for my scripting work. It all means practicing the craft, and then practicing the performance.
There are a lot of skills you receive when you
train in improv that help you make a volunteer a part of the spotlight. You're not only ready for the unexpected, but you've trained to make everything that person does a positive part of your show. Your spectator/volunteer can do almost nothing wrong but almost every choice is the right one. So, I'm going to say that trained improv really, really helps with that specific goal.
I am, to reiterate, talking about
trained improvisation. I am talking about
planned motivation for using that training. Also, I still have a beginning, a purpose and an end-goal even if much in the middle is made up on the spot. I would have missed a lot of great moments if I avoided any improvisational elements at all (Rhys-Davies). I would have no consistent character, act, or purpose as a magician (besides "look at meeeee!") if I did not prepare a great deal of material beforehand.
In short, there have been other times when absolutely odd things happened that just can't be planned for. I was already trained with the instinct to make that a part of the show.
I can't fully agree or disagree with Steerpike. I very much believe the magic show needs planned purpose. It needs a planned theme. It needs some sort of preparation of the sort that has nothing to do with the effects. It needs the things that come with preparation. The rest, I think, comes down to different schools of theater.