If the directions in the kits say not to wash, don't wash!
But this question in general has many professionals who don't even agree whether to prewash fabric or not. I don't like to prewash fabrics, mostly cuz of the time and effort involved in ironing etc. Keep it simple is my motto. But I understand why some people do, allergies. One professional, I believe it is Sharon Craig, washes everything and then starches or puts sizing in, irons, folds.... way too much work for me.
And many people like that there is a bit of shrinkage in a finished quilt, it gives it that 'quilted' look.
I use the color catchers also for laundering the quilt when it is finished and it works great.
hugs sue