Your question is a good on Skhf. What I found after some time as a quilter that if I LOVE the material I will purchase that 2 -3 yard cut. From time to time I will also go by how much is left on the bolt. If I buy all that is left and can get a good deal on the yardage, I'll buy it all. I once bought 10 yards of something that would make a good backing but because it was in a bargain area and I took it all I got it for $3 a yard. Really nice quality and something appropriate to use on the back of my scrappy quilts.
I also have to say that I have a large enough stash that I seldom buy fabric just because I like it any more. I am trying to discipline myself to use what I have and only purchase what is needed, when it is needed.
Happy shopping and enjoy this craft. You will find your passion and learn so much as you try new methods of being creative.