This is a snippet taken from the Blog of producer blog. It was released on GamePress so there is not link.

The big differences from Wii MotionPlus to non-Wii MotionPlus are the one-to-one backswings and the ability to force your player to hit a forehand or backhand.   This is something the best pros in the world do.  You’ll see Roger Federer or Rafael Nadal run around their backhands so they can get to their stronger forehand sides and rifle winners across the court.  The default mode of the game takes care of your backswing for you but with Wii MotionPlus, you are now in complete control of your backswing, allow you to hit that forehand like Federer or Nadal would.

The tennis experience also grows with added shot depth and pin-point ball placement.  Wrist rotation is more significant because it detects at a higher frequency and you can continue to curl the ball even after you make contact.  I’m sure like many others, when I have a racket in my hand, one of the first things I do is spin it, just like the pros do.  And with Wii MotionPlus detecting racket rotation, my in-game character can spin its racket too.

The aiming of the ball is taken to a more literal level so where you finish your swing is where you’re going to place the ball.  Whether you’re going cross-court or down the line, you’ll feel that difference with Wii MotionPlus and you can now control every inch of the court with precise ball placement.