gale

I don't prewash because I have a lot of precuts (other than fat quarters) and don't want to end up having to buy new yardage to use with it.

M.I.Late

What I discovered is this:

Prewash - Avoids surprises like fading, bleeding, unwanted shrinkage. Also when quilt is washed later, it maintains the same appearance as when it was new. Also, the manufacturer doesn't always get the fabric folded and rolled onto the bolt square so this gives me a chance to re-square it before I refold it. Can be an inch or more off in a single cut. (Hold it selvage to selvage let the fold fall, is there a diagonal "bubble" in the fabric? If so, slide one of the selvages right or left - when it hangs completely flat, it's right. Now look at the cut edges again. 85% of the time, I've lost some usable fabric from the original cut. Can't discover this unless you prewash.
So strips you cut, may not actually be on the straight of grain and sometimes this shows.

Not prewashing - Risks surprises above, but when washed gives that aged, crinkly look that many quilters love.

As for me, I put far too much time into the piecing and quilting - I don't want it all ruined by a nightmare surprise - it's just not worth it.

JanetLovesSewing

I prewash because when I started sewing clothes some 40 or so years ago, fabric had no problem shrinking or bleeding on me. I still don't trust the fabric industry enough to cut without prewashing.