Interesting topic. I put it in the personal preference category, but SA and others are right that just because Groth can do it, doesn't mean it is a good idea for rec players. For one thing, pros have grooved their motion. They could probably hit it with their eyes closed.
I know that I personally find it difficult to watch the ball to impact on serve but I do seem to serve better when I do. Maybe you lose a tiny bit of pace though, depending on your motion.
For most players, I would say it is better to try to see it through impact. If it doesn't work for you, you can know plenty of pros don't watch it either. You better believe they watch it through impact on ground strokes and volleys though, the odd Nole pic nothwithstanding.
I know that I personally find it difficult to watch the ball to impact on serve but I do seem to serve better when I do. Maybe you lose a tiny bit of pace though, depending on your motion.
For most players, I would say it is better to try to see it through impact. If it doesn't work for you, you can know plenty of pros don't watch it either. You better believe they watch it through impact on ground strokes and volleys though, the odd Nole pic nothwithstanding.