I started out buying tons of fat quarters. But as time passed when it came to using them they were mostly good for scrappy quilts or a paper piecing project or tote bags. All of which I rarely made.
Now if I see a fabric that I think is "interesting" I buy 1/2 yard. If I see one I "like" a lot I buy 1 or 1 1/2 yards of it. If I see a fabric that I "LOVE" I buy 3 yards. That way I am assured of being able to use them happily in a quilt.