it depends on the type of quilter you are - if you like the scrappy look then FQs are enough.
i don't do the scrappy thing and i mostly make wallhangings (which BTW doesn't mean they are small i've made some that are over 7 feet square) and the minimum i purchase is 3 yards.
i would rather have a little left over after a project then have to put up ads looking for more.
when you have a stash it could be 2 years or more before you pull that fabric out to use it.