Pros:
1. Gets all those darn tight wrinkles out!
2. Removes a bit of the 'finish' applied by the manufacturer, making the batting more comfortable to handle.
3. Slightly shrinks cotton batting. (Although I have not found that it leaves my previously unwashed fabric quilts with less than the traditional look I prefer after quilting and washing, as PaperPrincess mentioned. I like the 'traditional' way my quilts look after they 'pull up' abit, when the batting is washed first, but the fabrics aren't.)
Cons: Hmmmmm,
1. Because I shake the damp-dried batting out over the furniture over night, just before going to bed, it does sort of make the house look like it's all under dust covers!
2. You need to be alert when "washing" batting because you are actually just soaking it. If you agitate a batting just once, you will never make that mistake again! Load the batting into your washer; fill with cold or lukewarm water; turn off the machine; massage the batting a bit by hand, pushing it up and down gently to be sure all is wet; let sit several minutes; drain and gently spin the water out; turn off the machine; remove batting.
3. The same goes for "drying" batting; you must remember to use the "air dry" setting and remove the batting from the machine immediately afterward.......takes being on your toes (in my world!) and not getting distracted.
I no longer use polyester batting, only cotton or wool, but if the batting was plyester and in a package rather than on a roll, I use this same process for wrinkle removal.
Jan in VA