I have recently begun hitting a foam ball against the wall to improve my volleys, since I have been playing more doubles lately. I think the benefits are reduced noise and it is not so hard on my arm joints, since it is not as heavy as a regular ball. It is a lot easier to keep the volleys going too, since it's more forgiving.
I do overheads, serves and volleys against a racketball court wall. I think it's a great cardio exercise, and I have seem some improvements on my volleys; I am more aggressive at the net now.
Are there any drawbacks to hitting with the foam ball, if I still hit with the regular balls from time to time?