I do not prewash.....WHY......'Cause I'm an old woman and I would rather wash them afterwards because I like the look of them afterwards.....don't have enough time left for all that washing and ironing, want to make as many of them (quilts) as I can so my children will have more to fight over.
If you prefer washing first do that! If you don't want to wash first Don't!
To each his own and only you can determine what you, personally, want to do.
Just enjoy your quilting......doesn't matter which way you do it, just like the toilet paper thing....you know, out facing or inward facing....it will still work.
delma