I am a big believer in prewashing everything, so I don't buy jelly rolls. I had one bad experience from a quilt being ruined by an unset red and it reinforced the need/desire in me to prewash. To be completely honest, I did prewash the the maroon that ran but it wasn't enough to stop it. I should have (and now do) further tests before I use it. There's more to the story and a picture of the offending fabric in this thread:
Cutting the selvages off fabic
It is my experience that backs shrink quite a bit and/or are not what they are marked to be, in addition to usually being cut badly so I always buy half a yard more than I want. I wash on warm and dry on hot. Whenever drying fabric though, you want to get it at the moment it is mostly dried and not dried to a crisp or else it can be difficult to get out the dried in wrinkles. If you get it at the right moment it barely takes any ironing at all. A moment later and you and your spray bottle become best friends
Recently I bought a lot of fabric through Craig's list and some from the goodwill and have been doing a lot of prewashing. A whole lot... 30 pounds of fabric worth done, maybe another 20 pounds to go. I must be crazy. I really prefer just to throw in a couple of pieces in with my regular wash but I mostly work in scrap/charm quilts where I collect a lot of small pieces of fabric so it is important to me that when I go into my stash it is ready to be used.
The worst things to wash are narrow width of fabric, jelly rolls would be a nightmare. As it is a 1/4 yard cut WoF always sheds, snakes, and tangles with itself and anything else it can get a grip on even if I put it in a lingerie bag. Fat quarters seem to wash in with the regular stuff just fine. Smaller than that and they go into lingerie bags.
If I can avoid it, I don't like washing lengths of fabric over about 3 yards. Even if I am using more than that I can usually sub-cut into 2-3 pieces. Over the years I've found that long pieces of yardage iron out better if you do the selvedge ends first for about 6-8" on both side, then I go back through the width. I use the ironing board to help me fold the fabric into quarters along the length and then fold the pieces to fit in my boxes.