I'm a pre-washer and have been doing a 'scientific' study. I've been measuring the fabric before and after laundering and have found that almost all my non-batik fabric has been shrinking about 2" across the width of fabric, and almost nothing across the length. Don't know how you feel about shrinkage, but you may want to wash the most color saturated piece. This way you can check for bleeding and if you measure before and after, find out if it shrinks.
I'm going to continue to pre-wash. I use cotton batting and like a bit of a crinkly look, but am worried about the fabric shrinking unevenly.

I tend to wash the deep batiks. they seem to run and have lots of extra dye. I always use color catchers when I wash a quilt the first time..

I love to iron, but normally don't prewash except for flannel. So far so good. No problems.

I've done both. One rule I follow is that it's either/or. Either it ALL gets washed or it ALL doesn't. I have had trouble with some older prewashed fabrics that ran like the dickens for 8 or 9 washes after the quilt was finished. Now I gauge the very intense fabrics and test the more vibrant ones. I always tend to wash batics because those tend to run.

I don't mind the washing part of pre-washing, it's the ironing and starching part I can't stand. I have pre-washed fabric for one quilt only and that was done because I wanted a smoother finish after washing the finished quilt. Did not like working with the washed fabric at all but the end result looked exactly the way I wanted it to!
I have made a couple of Kaffe Fasset quilts with his vibrant fabrics mixed with white and have not had any issues with bleeding from my unwashed fabrics.

OK, well now you know a soul who prewashes precuts. That's me. I prewash everything. I didn't always do it that way, but a long time ago, when I was making a "Mother of the Bride" dress for a very special lady, I wanted to wash it because I had used so much starch on the delicate fabric in order to cut it correctly (remember, we used scissors back then) so I washed it in lukewarm water. Well, the red in the sashing bled all over the front of the dress. What a mess! And here we were, a week before the wedding, and I still had to fit a couple of bridesmaid dresses for girls coming from out of town. The Mother of the Bride dress was a total loss; there was red dye everywhere. I had to start from scratch, meaning buy the fabric all over again, which meant I made no profit and actually lost money on the dress. I worked 20 hours a day, I barely slept, I hardly ate, I just worked on that complicated dress. When she came for her final fitting, I was terrified I'd have to do a lot of alterations again, but by using the first dress as a template, at least I avoided that. You'd better believe I prewashed that fabric! The dress turned out beautiful, the bridesmaids were fitted, and I stayed awake long enough to take photos at the wedding before I crashed, but I've never forgotten that experience. And I never send fabric to anyone that I haven't prewashed. I will not be responsible for someone putting a quilt together and my piece bleeding and ruining all that work.

When I get tired of ironing, and especially if I'm just starting a big project, what I will do is take my prewashed fabric (I don't mind washing) and starch it so it's quite moist, and then I take it to the local dry cleaners. I have an arrangement with them. They will run my fabric through their "mangles" and iron them in no time flat. (Mangles are big machines with double rollers that they run sheets and things through to iron them for hospitals and hotels and places like that. I know. I used to work on a mangle in a laundry -- eons ago!) No pulling or stretching of the fabric. It just rolls through the mangle, and I've never noticed that it's warped in any way. Then I can go straight into cutting.

I'm doing what's comfortable for me with my quilting. I'm not saying you must do the same. Nobody made me the Quilt Police, and I don't want the job. I'm just sharing experiences.

Cheers!

I don't prewash either. I always color test a piece of the fabrics in warm/hot water for 24 hours to see if they bleed though. Didn't test one time and ruined a quilt, now I always test before cutting.

i'm a half & halfer---half the time i pre-wash the other half i don't bother---it really depends on the fabric- if i have fabrics (like Kaffe's) that i simply am not sure about i simply test to see if they are going to bleed---simply spritz a small corner with water- rub it with a paper towel or piece of muslin- if color comes off you have a bleeder- better wash---if no color comes off- good chance you are safe.
i tend to prewash if the fabric is stiff- doesn't really feel good- or has a funky smell to it- or if it's a hand-dye- or batik with deep saturated colors-
i always test reds, deep blues/purples...if they are not bleeder's i don't worry about it-
and some flannels i pre-wash many i do not- just depends on what they are going to be used for- i use Benartex double sided flannels which are a bit more expensive but oh so worth the extra$$- i've never had one shrink enough to cause any problems- the only cottons i use that shrinkage may be an issue are homespuns-and i've made a few great home-spun quilts without pre-washing- since the batting and quilting also play a part in how much a fabric will shrink....anyway- when in doubt---test for color-fastness- other than that- 'don't sweat the small stuff'

I never pre-wash and have never had a problem.

It's not just less expensive fabric that will bleed. I had a Jinny Beyer pink fabric and have never seen anything bleed like that did. I have found that if I let fabrics dry then iron then put into very hot water most won't bleed any more. The Jinny Beyer fabric I had about 9 changes of water. It was still bright. My teacher said it's what they call overdye. I'm just glad that I persevered because I hate to think what it would have done to my quilt.
BTW I wash everything.