Wall training is the best training you can get when you train by your self. You only need a ball and a wall. In the modern game it is vital to have good passing and receiving and wall training is perfect to improve your passing and receiving of the ball.
The wall never makes a mistake. If you give a good pass at the wall, you will get a good pass back, and the same if you give a bad pass at the wall it will give you bad pass back.
Wall training is all about reputition, you have to do the same training again and again. There is no better mechanism to maximize repetition and to build the muscle-memory necessary to master key skills.
The wall is the perfect training partner, he can play with you for hours every day and he never gets tired.