why I do practice paintings

I often think, am I wasting time and material doing practice paintings? as I was working on my latest painting I noticed something off with it and I wasn’t able to pinpoint what the issue was. I studied the practice painting < just staring at it, and it hit me. I have too much green in it and it was washing out the effect of light I was going for, so with a few brush strokes I was able to add a wheat field with a golden color and my problem was fixed, when I worked as a mechanic I would come across problems that seemed to not have a salutation and I would stay up at night trying to figure it out, most of the time I could.