I can convert yardage to precuts and visa versa. When I want to make a quilt, I pull fabric from my stash, then purchase as little as I can to make it work. I desperately need to reduce the amount of fabric in my house, so I always shop here first. My problem comes in when a pattern calls for 1 1/8 yards and I tended to buy just a yard when I used to purchase 'just because'. The quilt I'm cutting out Friday will have to be cut very carefully for that reason.
I don't think I've ever followed a quilt so exactly that I used the fabrics it called for. I use patterns for instructions and choose my own colors/prints.