Although some quilters never pre-wash their fabrics, I nearly always do. I don't want any surprises
My story: Assuming that wall hanging will never be washed isn't safe. I had a sample hanging in a store, there was a fire down the way in the strip mall. My quilt was smoke damaged. The conservator they consulted told them to dry clean everything, so they did!
What if your quilt contains several
different unwashed fabrics--and some of them shrink more than others?
Uneven shrinkage could cause puckers and distortions the first time the
quilt is washed.
Some quilters intentionally use unwashed fabrics to
assemble a quilt because the puckers left over after the first wash give
the quilt a vintage appearance. If vintage isn't the look you're going
for it's best to pre-wash your fabrics.
I use a laundry additive called Synthropol. (What is Synthrapol? It is a special detergent used in pre-scouring fibers before dyeing, and in washing out excess dye.) Add a capful to each load of fabric keeps loose dyes from depositing on other fabrics during the wash.
I press everything before I fold and put it away, I like them ready to cut when I'm ready to use them.