You always hear stories of the 3 year old who hit the ball against the wall thousands of times. It's normally a success story.
Either way it builds good discipline because it's so darn boring. It's much like playing a grinder to hits a repeatable ball that lulls you to sleep, So... you have to keep your mind engaged on what you're doing/working on because there's not much external stimulus.
Enjoy the simple pleasures of tennis like the feeling of the ball on your strings and your muscle systems working together.
Hitting against a wall, among other isolated drills, is a great way to bring the focus on your body mechanics that are often forgotten during the dynamism of a match.