Originally Posted by BKrenning
They sew the strips onto a foundation because there might be some bias cuts. With scraps, it's harder to tell what is on grain or off grain so the foundation keeps the strips from stretching and causing your blocks to go all wonky. Also, some string blocks are made on the diagonal so all the outside edges when squared off will be bias edges.
I guess the only reason I haven't run into this problem so far is that I can usually recognize grain (thanks only to an excellent bifocal prescription from the local eye-guy). So I will definately keep this in mind.
Thanks very much for your help everyone!