Most of my original "stash" was scraps from clothing I'd sewn. I only bought fabric for clothing when I had a specific project in mind... Well, sometimes I ended up not actually getting around to it. Then I lost my stash in a move. Suddenly I felt bereft and started buying whatever I could afford, just I would have something to sew with if the urge struck me. But I wasn't as picky as I should have been, and ended up with some fabrics I just didn't really like that much. Plus, friends and relatives started giving me their scraps and unwanted stash - several old ladies said "I just don't sew anymore, would you be interested..."
So I ended up with a lot of fabrics that are not really "me". Now I am working on using up/getting rid of what doesn't fit my current vision for the types of quilts I want to make, and buying more intentionally, filling out the color gaps in my stash, buying better quality, etc.
But I like having a stash, in part because I live out in the country, and it wouldn't be practical to run into town every time I had an idea about something I want to make. I'm saving gas this way...really. :)