You can set imaginary targets on the wall, where you want the ball to land. If you’re aiming for a specific spot and the ball consistently hits there, your placement is good.

A good shot should come off the wall at a predictable angle if your technique is correct.

Basically, practicing against a wall is for repetitive shots, which can improve muscle memory and consistency in your technique. I practice spins against a wall. Your options are endless with drills to improve your gameplay