I tried doing a very little bit of stash-building my first quilting year but I haven't used the fabric and I no longer buy anything until I am starting a project.
I have done maybe 16 projects now and I have saved all the leftover fabric. Sometimes I have a lot of leftover because I am not sure how I will use each fabric in the quilt and I buy to have enough.
Sometimes leftovers from another project can go into a new project but mainly it is piling up, and I am going to have to get seriously scrappy!