If it's washable, I wash it before incorporating it into anything.

Had enough "surprises" to not trust ANY fabric from ANY manufacturer.

If you normally pre-wash, I'd say wash the yardage before cutting it, rather than washing cut strips, which will fray. I pre-wash everything. I'd rather have any shrinkage and running occur before the fabric is stitched into a quilt.

I'm a pre-washer too. I don't like surprises, and I also don't like handling fabrics that are full of unknown chemicals and (probably) pesticides. I don't currently have any sensitivities to these things, but sometimes these things are "bio accumulative" and you can BECOME sensitive. I figure the less chemicals I'm touching and breathing, the better.

What few pre-cuts I've purchased, I pre-washed but used a lingerie bag and tacked a few strips on the ends and middle to prevent tangling. I starched them lightly and ironed them by placing them on an old pillow case. I prefer to purchase yardage and cut my own, much less expensive and if they are off by measurements it's my fault and I can only be mad at myself.

I prewash before I cut. I don't like surprises after I have finished a quilt. My method is unusual. Don't know if anyone else does this. I don't like wrinkles and thread fraying--so--. I immerse the fabric in hot water and let it soak for a couple of hours. Then I rinse it as many times as necessary for the water to be clear. Finally, I hang the fabric over a line and let it dry. There is no ironing or fraying. The sizing and chemicals have been washed out. Some will believe soap is necessary or that tumbling in a dryer shrinks the fabric more--may be true. I won't argue, but this method works for me.

If unwashed fabric doesn't bother you I'd leave it. I prewash everything because if I work with unwashed, I get itchy hands and eyes and sneeze a lot. Must be the chemicals. I quit buying precuts for this reason and am trying to use them up.

eta: I never used to have a problem with the chemicals but started to in the last few years.

I wash batik fabrics. Don't have time with others as I use immediately I get home.

I came across a video on utube for prewashing precuts. She gently places them in water and uses a salad spinner to get excess water out, then dries them flat. I'm a relatively new quilter but I've had 3 fabrics that have bled unbelievably. I'd rather treat the fabric with Retayne than cross my fingers when something I've made hits the wash. The video is from SewVeryEasy in case I haven't done the link correctly.
www.youtube.com/watch?v=02S22-ri2EQ

I prewash everything that has x amount of cotton in it. Some fabs like cotton knits I will wash (and dry) twice before using it.

I have to prewash first as doctors orders since it has lots of formaldedyde in it and it makes my hands sore and cracked and also not good to breathe then instead of starch I spray and iron with fabric sizing and iron I also pick up the empty bots at fabric stores cut in half fold and store my fabric on that and works great for me