It is completely your choice on whether or not to prewash. I was raised prewashing, still do it for most of my fabrics but am aware it takes time I could be piecing. However, I have skipped prewashing occasionally and have had some fabrics run when washed. Supposedly there are color guard sheets you can purchase to minimize this from happening....but all my stash is already washed, so it's easier for me to keep up with my habit. Best of luck!!