First off - I only buy fabric for specific projects - not a stasher here. Usually only buy yardage. I am also a pre-washer. Probably a hangover from garment days BUT my reasons are as follows:
Yes, bleeding/shrinkage can occur. I'm really not overly concerned with the shrinkage factor. I use 100% cotton batting which I do not prewash, so my quilts are going to shrink when completed anyhow. Bleeding - yes, that's a reason to wash.
I wash my fabrics in the machine, warm water; detergent; no fabric softener. Dry in the dryer until completely dry. I am a firm believer that the way the fabric is folded/wound onto the bolt is nowhere near close to being on-grain. I like to work with my fabric as close to on-grain as possible. I think you get more accurate cuts and then sewing as a result.
I also iron my fabrics with starch. Have migrated to Sta-flo 50/50 with water. Use in a spray bottle and mix a bit at a time. I use starch on either front or back, don't really care. I find that if I let the starch absorb into the fabric for at least a few seconds there is no flaking when ironed. Generally don't get very heavy handed with the starch unless I'm working with really small pieces or bias edges.
When I go to press my fabrics I spend a reasonable amount of time hanging/wiggling my selvage edges together to get the unironed piece of fabric as close to flat as possible. Then I lay it flat on my ironing surface (in my case, my craft table covered with folded towels) and smooth until the fabric is as flat/smooth as possible. I usually start in the center of my yardage, pin if necessary to hold in place if I'm dealing with a large amount of fabric. Work my way out to the ends smoothing and then iron with starch. Thats the point where I square off my end to start cutting the balance of my pieces.
I find that taking the time going through this process yields in much more accurate cutting. When your cuts are more accurate, your sewing becomes more accurate - at least it does for me.