I always wash, for all the reasons stated by everyone else. But also, once, I was trying a new batting and I washed a quilt it came out really really wrinkled. Low and behold, the batting was supposed to be prewashed to size it. I gave the quilt anyway and told the recipient, I was trying a new batting if you would like a flatter quilt, I can make another one. She loved it. But I know if she had washed it, she would have thought it was ruined.