California became one of the first states to enact legislation stating that marital property stops being earned when the parties began to live separate and apart. This has been our rule for about 35 years.
In a community property state like California and a number of other western states, the rule made sense; why would we divide income and assets once the two spouses are not working together in some semblance of a shared relationship. Community property recognizes that courts aren't good at valuing the services of the husband and wife, such as where one may work and the other cares for a home. When it became a state, California decided that the value of the parent staying home to raise children could have the same value as the spouse who went to work knowing the home was secure, and selected the community property system. Alright, so that type of relationship may be a fiction, but we also don't want to litigate these issues, so we have a general rule.
As California had the minority rule, some experts have speculated that judges tried to find exceptions to the rule, perhaps to bring us back in line with other states. As a result, we have had varied outcomes when these cases are litigated. Sometimes living separate and apart had no meaning because of the exceptions created - the most famous was a doctor who wasn't living separate and apart on his boat with his girlfriend, in part because he still took his laundry home for his wife to do. [His wife wanted half his earnings after he moved out, and the girlfriend tried to claim the other half.]
One battlefield has been over situations where the parties continue to live together, but one wants to claim the marriage was over, so they were living separate and apart. Last week, in the case of Marriage of Davis, the California Supreme Court decided that "living separate and apart" means that the parties have to be living separate and apart to be separated - in other words, you can't keep living at home, earning income and acquiring assets that you don't have to share with your spouse. What a bizarre outcome - judges who actually got it right. Of course, to muck it up they had to insert a footnote leaving an opening for more exceptions.
I vote for bright lines, like "living separate and apart." Sharp lines limit litigation, which is usually a good goal. Appellate judges live in ivory towers, and don't have to answer to clients when the law does foolish things.