I prewash all my fabric, I don't purchase jelly rolls so no problem there. I recently purcheased some fabric by South Sea Imports from a quilt shop, it was green and I put it in a basin of hot water to soak to see if it would fade. I ended up soaking a washing it six or seven times before it stopped bleeding. So you never know.

I prewash flannels and batiks if when tested they run. I always use a color catcher when I wash my quilts at the end. so far i've not had any problems with not prewashing.

pre-cuts are always an issue when it comes to pre-washing/not pre-washing. ...
most of the shops, manufacturer sites will tell you with today's fabric making techniques it is no longer necessary to pre-wash. pre-cuts are cut with the belief they will NOT be pre-washed. they will shrink a little and no longer be the pre-cut pieces you thought you had. some people no matter what have to pre-wash, if that is the case i would avoid pre cuts at all cost and if somehow it was necessary for me to use a pre-cut i would put them into a mesh bag wash very gently (just enough to remove the chemicals/sizing in the fabric then i would wring out well and iron dry.
when i purchase new yardage i pre-wash it if it is a color that commonly bleeds (reds, blacks) i pre-wash if the fabric has a funky smell or a funky feel to it. there is something very nice about the feel of freshly laundered cotton fabric. then press with a little sizing or starch if needed; but if the fabric is damp when you are ironing it you should not have to add anything.
oh and i ALWAYS pre-wash if it 's batik's or hand-dyes.
i don't worry too much about it if it is a printed fabric from a (big) manufacturere-but i do test to make sure nothing is going to run.

I prewash everything. I'd hate to work so hard on a project and then have it bleed or something. Many have used color catchers or haven't noticed a problem, but still...I'm nervous! :D

I prewash everything. I'd hate to work so hard on a project and then have it bleed or something. Many have used color catchers or haven't noticed a problem, but still...I'm nervous! :D

If it isn't for a swap I don't prewash. The only exception is batiks..always prewash. I think the prewashed fabric is more stable and easier to work with.

I used to wash all my fabric but I no longer do. I really prefer the "old fashioned" wrinkly look in quilts, plus I prefer the "feel" of the unwashed when working with it. I do wash flannel, unless it's for rag quilts and batiks before I use them though. I really think it's a personal preference.

if you search on the su subject you will find many many posts on this subject.

I don't usually prewash anything, except flannel. But I do wash my quilts before I gift them to get the chemicals out of the fabric. :D

I am working on a lap quilt now that I made of a jelly roll and will be backing with flannel. I did wash the flannel because I know how that shrinks but not the jelly roll. I figured I'd end up with a lot of fabric lost in the fringe. When I am completely done with the quilt, I'll throw it in the washer (with color catchers) and then in the dryer and pray for a good outcome!