I open it up as well. Not only to help get rid of the crease but to ensure that no creases capture loose dye or fail to release the loose dye. As a LAQ I also greatly prefer prewashers to non. There is nothing more awful than to spritz out a mark of water soluble marker only to see the fabric you spritzed start bleeding.
To DebraK, with wide back I also open up as much as possible and layer it in the washing machine like I would a sheet or any other large item. Unfortunately there is no easy way to do wide back. They are a pain no matter what. I try to take it out prior all the way dry and then iron it (also a pain!). It is easier to fold if you enlist a helper but if not I just fold the best I can.