You can see how much more challenging it is to keep your drives accurate when you take away the sidewall. If you want to learn how to really keep the ball perfectly straight try incorporating the drills above into your solo routine. I try and aim for the middle line and see how many drives I an hit into the backdoor in a row. If you're a lower level you could try and see how many times you can hit the door in a specified amount of time vs. consecutive.
Good luck and enjoy!