I never thought about until I did my last quilt. The Warm and natural had wrinkles in it galore. I used my hands to try and smooth it out. I didn't end up with wrinkles after quilting, thankfully. I think it would have saved me a lot of aggravation if I had iron the batting.
I iron the top and bottom so I might as well iron the batting too. Less wrinkles is always good!!!! LOL!!