The most common reason for divorcing spouses to continue living in the same house is because neither wants to leave their children behind. When a parent leaves the home and moves to another location without an agreement for parenting plan in place, they are essentially ceding physical custody to the other parent. Physical custody is simply defined as who the children reside with and unless there is a plan in place, if only one parent lives in the children's home, then that parent necessarily has physical custody (it is possible for a parent to move out with the children, but this is unusual except in cases of abuse).
While many parents will fight over who can remain in the home during this time period, this argument is a distraction from the reality that eventually divorcing spouses will live separate and apart. It makes more sense for the spouse who will eventually move to begin investigating their other options as soon as possible, and for parents to work out a realistic parenting plan prior to that move. Rather than use this argument as a ploy to fight over the children, discussing practical resolutions will focus both parents on how much time each will spend with their child instead of focusing on what they are losing. Divorce will never leave each person whole, but to the greatest extent possible parents should strive to keep their children from getting caught in the middle of any disputes.