Beat looks like it's referring to the timing...

I think his movement is super efficient though...so the idea seems to be you don't need to rotate your body into the ready position so fast, you can wait for the incoming receive to decide. So if it comes to your BH you can just pivot by moving your left leg out of the way, and if it comes to the FH it should be basically just right leg stepping to the right and then you'll be in position to loop...

Lol haha that's true....he's RSM the footwork God after all!

I think it could be part of some pattern plays which limit your opponents directional choice though. For eg a very high quality sidespin pendulum to the opponent's BH short corner would be very hard to control down the line to the deep FH, so most receives will be in the BH corner where you're already waiting to pounce on. 

I don't think it's a Jpen thing, it should be applicable for whoever wants to attack with the forehand after the serve.

It seems like it's more of an optionality provided by the narrow stance after the serve, as both legs are near the backhand corner. So for eg if you had to cover deep FH you would just need to move your right leg to the right and you would have covered it. If you had to pivot then just move your left leg to the left. So pretty much you can cover almost everything with FH with 1 or 2 steps at most. 

If you were in a wide stance directly after the serve with the right leg near the centreline after the serve then it'll take 3 steps to pivot rather than 1 which is a lot slower (as RSM demonstrated). But of course those who go back to wide stances immediately after the serve do not usually intend to pivot but rather prefer to take balls with their backhand.