Get two or more quilters in the same room, and soon you will witness the Pre-Wash Debate. I am not a purist and I think both sides have some valid points.
Here is a bin of brand new fat quarters:
Some quilters feel that the fabric is easier to cut when it has that fresh-off-the-bolt crispness. With modern technology, we do not have as many of the problems with shrinkage and bleeding as in days past. When I worked in a fabric store, on a slow Saturday afternoon, I would pick out fabric for a new sample and start cutting right away.
Here is a pile of washed and folded fabric:
Some quilters are sensitive to the dyes and chemicals used in processing the fabric, and who knows what has touched the bolt before it gets to you, so I am leaning towards pre-washing everything. Most of my quilting is done with the intention of sending the finished project to charity, or as a block exchange with other quilters. In both cases, the preference is for pre-washed fabrics, so there are no surprises.