@Bagumbawalla
I've come across sources & other coaches who do advocate it. I do it myself quite easily. My primary Fh grip is a strong EFh (an E+). However, for chest / shoulder-high balls, I will switch to a SW grip for topspin. Especially if I am playing against someone who hits a lot of their shots that bounce high.
I've seen quite a few rec / intermediate players who are quite capable of doing the same thing with their grips. Will often switch to conti for squash shots, tweeners, Bucharest Backfires, etc.
Not everybody's cup of tea but, for some of us, it is not really an issue -- certainly not what I'd call overkill.
S/A, I realize that you are one of the best-informed and knowledgeable experts when it comes to tennis (and some other things).
I also realize that if something works for a player, and they are happy with their level and quality of play- there is no need to force change on them.
I suppose I am the kind of idealist that would have suggested that Ken Rosewall or Steffi Graf do more with their backhand topspin drive.
As everyone is aware, the further one progresses in tennis, the faster and more intense the sport becomes- time become a valuable commodity. Every simplification, every step saved, every decision refined, every reaction improved, are just so many ways to uncomplicated and refine ones game. Obviously, on the "public park circuit" all this may be irrelevant,
but when someone asks the question, my basic philosophy is to simplify.
Yes, there is a guy I sometimes hit with that has 3 different serve tosses and grips. He serves very well, but I always know what shot he is going hit, and where. His serve could be improved by simplification.
One volley grip should be enough. One, possibly two, forehand grips should be all one needs, same with backhand- two If you drop the second hand to slice- one service grip. Much more than that is just time and attention subtracted from ones game.
Yes, there may be some pro players that one can site,who do some wonky things, but, for the most part,
most pro players have worked out the inefficiencies of the game. Every shot is much like the rest. They don't choose between 3 service grips, change volley grips between forehand and backhand, choose between a variety of forehands and backhands.
Obviously, on the playground, we are not teaching old geezers to become pros, but I think it may be simpler for them to master one single stroke than five subtle variations.
In the case of moving up the grip to volley, a little lead in the butt-end of the racket may make that extra step unnecessary. Simplification.