Picture this scenario:  You’re playing a match against an opponent who is solid from the baseline, however, his serve is weak and slow.

You’re trying to take advantage of his weakness but you’re making way too many errors on the return of serve.

As you may know, it’s tougher to be consistent against a slow ball as compared to someone who hits hard.

When you’re playing against a hard hitter you can get into a rhythm,  there’s not a lot of thinking, you’re sticking the racquet out there.

Remember this, it takes better stroke mechanics to hit a slow ball consistently in the court.

There are 2 Key points to remember:

#1.)  at the low point of your backswing the racquet should be closed (or facing down)

#2.) Swing from the shoulder with as little forearm and wrist movement as possible and your racquet is guaranteed to be vertical at contact.

After contact, the hitting arm relaxes and comes up across the body, at this point it doesn’t matter if you roll the forearm and wrist the ball is long gone.

However, if you’re trying to roll the forearm and wrist in the hitting or contact area, it’s going to be hit or miss, it will be very difficult to develop confidence in hitting away against slow serves.
Reference: Tom Avery