IMPO...while I wouldn't involve kids in most situations, there is nothing wrong with them seeing a parent sleeping on the couch. It CAN teach them that sometimes people need some space, and it's ok to take that. It CAN teach them that you don't walk out just because something gets difficult. It CAN teach them that it's ok to stand up for yourself too. It all depends upon how the parents handle the situation with their kids.
I don't think that I would recommend sleeping on the couch and not reassuring the kids that things will be ok...that could be scary for them.
I always knew that when my Dad was on the couch that they'd had an argument of some sort...but they were working things out, but they also let me know that.
