I pre-washed Hobbs 80/20 last week with fine results. If I remember correctly, the instructions for that batting pre-wash is to submerge in water for 20 minutes, which is what I did. I did not agitate, but I did the spin cycle, stopping and checking once or twice as it went to make sure it was not stretched. It came out of the washer great. I then laid it flat on the ceramic tile floor. It did not take long to dry and was not wrinkled. There was no shredding. The piece was about 60" by 70".
In the past I have washed larger sections of Warm and Natural in the bath tub. it is heavy work, but it has turned out fine.
I do not care for the crinkled look and do not do close machine quilting, so with cotton batting I pre-wash. If a batting says on the package to expect 3-5%, that is something I do NOT want. I also pre-wash all of my fabrics before construction.
Lots of quilting teachers don't say to pre-wash batting, and many also don't pre-wash fabric. There is too much at stake for me to take chances.