I think that the batting that is needle punched is able to take a soaking before use better than the regular cotton batting. That, at least, had been my experience. The needle punching makes the fibers interlock and not come apart as easily when they get wet. I stopped pre-washing my batting as I didn't feel it helped anything and might actually make things worse, it it started to turn to mush in the machine. If you have chemical allergies, then that might be a reason to do it regardless.
John