I think it is a personal preference. I wash everything before I use it. I like to know that any bleeding or shrinking has already occured before I put it in a quilt. Some people really like the crispness of new fabrics. I iron mine with some magic sizing before I cut it up and it gives the fabric a nice crisp feel.

I wash some fabric - especially fabric that has been in my stash for a long time and dark colors and red. I don't mix fabric that has been pre washed with those not pre washed.

I always wash the fabric as soon as I bring it into the house unless it is going to be used in something that will never be laundered. My washer has a pre-wash cycle. I throw the fabric in that on warm water and no soap. It wets it, pretends to wash it and then spins. I then throw it in the dryer. I always include one of those sheets that catches any bleeding. About 50% of the time there is some color in in. Most of my quilting these days is for Linus and it is a good idea to make sure the fabric is free of excess dyes and dust.

If it isn't a really good quality fabric or has strong colors, I wash. I use to wash everything, but spent so much time doing it, I started to skip it, and haven't had any fabric run -- yet--but I am aware of the possibility-so, like I said, I wash if I think the color is strong and always use color catchers when washing the quilt upon completion. Only time I had running was my first attempt with flannels-made a rag quilt with deep purple, lavendar, light green and threw in some white. Even though I pre-washed the purple, and used color catchers when washing the finished quilt, the purple ran into the white. Live and learn! There have been so many threads regarding this, and I think it is just a preference. I am making purses now (taking a break from quilts) and never pre-wash.

I wash all fabrics I use, except precuts.

I rarely do but if you are going to use fusible web for applique, the web won't stick as well, if at all, it the fabric isn't washed.

I always wash my fabric. I also like to use magic sizing before I cut it.

Fabric that come into my house can't get past the mud/laundry room without passing through the machine. Only when it comes out of the washer and dryer does it qualify to enter the stash. I've read enough on this Board and other places to believe that, while it may happen only once in a while, there are fabrics that bleed/shrink/otherwise confound your best efforts to make a great quilt. I believe washing can remove or diminish some of these goblins and I haven't found any compelling reason not to wash every yard. (Although I admit a great quilt is still somewhere in my future.)