How not to pre-wash fabric

I've read conflicting advice on whether or not to pre-wash fabric before piecing a quilt. I've tried it both ways and haven't noticed a significant difference. When I made the tester last week, I didn't pre-wash the fabrics, but a quilt-pro at my office told me that it was particularly important to pre-wash flannels since they shrink significantly.

I calculated that I would need about a quarter yard of each of my flannels for the quilt so I cut off 10 inch strips and put them in the washer on warm without soap. This is how it came out:



After untangling the mess and cutting off the frayed bits, I ironed out what i could salvage, but I had lost enough that I needed to wash some more fabric to have enough for the quilt. This time I washed it in the sink. That worked much better.



Now all the fabric is pre-washed, ironed, and cut. Now I'm ready to start piecing the top of the quilt.