I buy when I see a Line I like, I'm an "Organized Quilter" so I don't do Scrappy!! It's just me but it's like fingernails on a chalk board!! I've seen many scrappies I love but could not make.
I always buy enough for a full size quilt in a line it may sit on my self until I see a pattern I love just for that fabric. I always make sure I know what I have so that if I do perchance need more I know I can search by fabric name. Have fun with your stash, I think the advise you are receiving is wonderful, don't buy just to buy. As you gain in quilting knowledge so will your ability to estimate what you need for certain quilts!!