I don't think it is unnecessary at all. I think it's a measure of skill, and it CAN help you improve. I also believe it is a MAJOR factor if you're a freelance artist who needs to pay for bills and maybe even university taxes. Also, have you ever heard of speedpaints? They're a great way to practice.
Maybe you meant to say that you don't rush when you paint, which can lead to a messy finished piece of inferior quality. If that's what you were trying to say, then yes, I agree with that.