Originally Posted by Nostradamus
this is nice, but if the ball loses all its fur, then it just flies thru the air too fast and is very hard to control still
True -- the re-pressurization process only makes sense under the assumption that the "fuzz" is still intact and that the ball is otherwise still playable. This comes into play more often with balls used for a ball machine rather than match play.
Balls used in match play are struck by rackets and against the ground hundreds of times in the course of a few sets. Generally, people only use a few (3-6 balls) during a match. However, with a ball machine, you may have 100 balls and only strike each a few times depending on how many times you reload the machine.
If you don't have the chance to make it to the court to practice with the ball machine very often, then you could go months without wearing down the fuzz on perhaps hundreds of otherwise "good" balls that go "dead" in a few days/weeks...
Tennis facilities and country clubs also have hoppers and hoppers full of gently used balls (often played once during tournaments) that coaches/pros use for teaching/practice. These balls often end up "dead" way before the fuzz is gone... It's literally thousands and thousands of dollars that go to waste...