With the help of my friend Kathie I re-found the articles about washing fabrics. They were written by Becky Goldsmith of Piece O'Cake fame. Here are the links:
Washing fabric -- part 1
Washing fabric -- part 2
One of the commenters asks her my exact question.
Becky's answer was interesting.
I know that many people use them and love them. I'm just not in that group.
Many, many of us have already bought them. So I'm going to make an exception for pre-cuts and used them unwashed. I'll wash the finished quilt right away with at least two color catchers.
And I'm still going to pre-wash everything else. Except for the grab bags full of scraps that I pick up now and then.