Alright. I confess. I don't pre-wash fabric. Used to. Not any more.
In a family of 6 I already spend far too much time in the laundry and at the washing line. I stopped washing fabric some time ago when I had to untangle lots of 20cm strips and iron them. Something else I'm not crazy about.
With charm squares and the advent of jelly rolls etc pre-washing has to be a questionable use of precious sewing time.
As for shrinkage, I can't quantify that. For me it hasn't been an issue. Of course there are occasional colour runs. This is my block #12
The red fabric in the centre top bud ran when I washed the block. Drat. But colour catcher came to the rescue. I put one sheet and the block in cold water and agitated it well. Colour catcher went pink. Block came out clean. Yay!
I leave you with a question. Why do you pre-wash?