I think most table tennis players have played a game or two with their opposite hand for fun now and then. But would you believe that for many beginning to intermediate players, using your non-dominant hand can actually improve your table tennis? Skeptical? Then read on.
While I would not suggest spending hours and hours trying to hone your opposite handed technique, I do believe that there are a number of benefits you can get from swapping hands from time to time, including:
For intermediate players trying to adjust your grip or basic technique, it's often difficult to successfully make the change simply because your muscle memory keeps telling you that the new way is wrong. Using your other hand to correctly hold the bat or play a stroke takes your muscle memory out of the picture, and lets you focus on whether the change actually works better than your old grip or technique. Of course, you probably aren't going to be relooping or performing other advanced techniques, but for grip changes and basic strokes using your opposite hand can be very useful.
Using your other hand also makes you focus on the doing the basics correctly much more, since you aren't able to compensate for bad technique with your usual bag of tricks. For example, as a right hander you might normally get away with hitting your forehand loop with your right foot in front of the left, since you open your shoulders and bend your elbow and wrist to compensate for your poor stance. You'll struggle to get away with that if you swap hands, and it will become very apparent why it's easier to hit the ball if you put your feet the right way around. That will give you extra incentive to correct your stance on your normal forehand loop.
You also get a different perspective of the table. For right handers, it's interesting to see how the table looks from a left handers point of view (and vice versa for lefties). If you are a right hander, try playing another right hander with your left hand, and notice the different angles of play, and how certain patterns used automatically by your opponent actually feed into your forehand and backhand strengths, if he isn't careful. It will give you more insight and a better understanding of where to put the ball the next time you come up against a lefty yourself.
If you are a much stronger player than your training partner or opponent, playing with your opposite hand can really level the playing field. If you are like most players, you'll have the ability to use only a very basic serve, and simple pushing and counterhitting. Your loop will probably be quite erratic. This can really force you to put an emphasis on winning via the use of better tactics - since all your usual weapons have been taken away, you have to really think hard in order to win with the limited array of weaker strokes you now possess. This can quickly let you know whether you normally go out and play brainless table tennis, relying only on your better strokes to win matches.
During a match, it can be handy to switch hands and keep hitting forehands from your normal backhand side at your opponent - the late Andrjez Grubba from Poland was a master at this! It's actually very offputting when your opponent does this - as I can attest from personal experience thanks to Craig Campbell!
If you are a coach, it can be very useful to use your other hand occasionally. After many years in the sport, you tend to forget what it was like when you first picked up a ping-pong paddle. That feeling of awkwardness and uncoordination is just like what a beginner feels. It certainly helped me keep my patience when any of my students was struggling to learn a new technique!
And finally - it's fun! Being able to take a break from serious play and play some ping-pong just for the heck of it, without any pressure or expectations, can be a refreshing experience. When you miss a loop or two with your normal hand, you often get frustrated and irritated, but when you do it with your other hand, it's just a good laugh!