The idea of changing your grip during a rally is a big no-no according to some players and coaches, and perfectly acceptable to others (probably depending on whether they change their own grip or not!).
On the world stage, Timo Boll appears to be one of the biggest grip changers, with notably different grips between his forehand and backhand. The debate still rages on various Internet forums about whether this is an advantage or disadvantage... Previous to Boll, Jan-Ove Waldner was noted for his grip changes to achieve certain shots, but it was fairly common to admit that he was a table tennis genius, and that changing the grip was perhaps not a great idea for the rest of us!
The main pluses of changing your grip during a rally is that it can allow you to better hit specific shots, such as Waldner's sidespin blocks, or Boll's heavy topspin loops. The main argument against is that you can get caught with the bat in the wrong position, making your stroke awkward at times. Both points of view are valid, but the importance of each will vary from player to player. Creative players who can think fast will often benefit from using grip changes to enhance their strokes, while those of us who don't have the same speed of though might want to limit the amount of grip changing we do.
Changing Your Grip During a Rally - My Own Experience
I have been a combination bat defender and twiddler for many years. I used to use very different grips for the forehand (heavy forehand grip) and backhand (extreme backhand grip), believing that as a defender I had plenty of time to change between the two. Besides, I was turning the bat to twiddle quite often anyway, wasn't I?
Then, for a while, I changed to attacking from both wings with speed glue. It soon became clear that I couldn't afford to be making such big grip changes from forehand to backhand. I had to spend a good 3 months or so changing to a neutral grip that allowed me to hit both forehand and backhand without getting caught changing grips so often. It was a painful process but worked much better for me.
As a bonus, when I eventually changed back to defending again, I kept the neutral grip, and found that I played much better this way. The neutral grip was much easier for switching between defending and attacking, and twiddling to a neutral grip was simple. I will still occasionally change my grip a little for a specific shot, but in general I find that a neutral grip is the way to go for me.
My overall rule of thumb(!) is this - if you routinely find yourself getting caught changing grips more than once or twice in a match, think seriously about trying to convert to a neutral grip. Those freebie points you are giving your opponent may just make the difference between defeat and victory. It will take you about 3 months and a lot of frustration, but it can be done - if I can do it with my own extreme grips, just about anybody can!
