Couples live separate and apart for several reasons and "separate and apart" has different definitions depending on the situation. There are "living situation" definitions and a definition that is applied when it comes to how the legal arena views it. In the legal arena, living separate and apart means the time at which you no longer live together as husband and wife. Generally this means when you no longer carry on the daily/weekly/monthly routines and rituals that would have been done while you were happily married. Examples of these routines would be eating meals together, sharing household responsibilities, maintaining joint financial accounts. During the separate and apart phase, you would likely be continuing to parent the children as you have in the past, but there is a definite shift in how you communicate and relate to one another on a daily basis. This shift from married to living separate and apart is unmistakable, based on the behaviour and feelings towards one another. No one has to move out of the bedroom for this shift to happen, although often this is a step taken to further enforce the message that perhaps may have been unclear up until this point. The date at which you decided to live separate and apart can, and often is, used as the separation/valuation date, the date at which assets/debts are divided based on their value on this date. If you are not sure of an exact date you can just agree on a date to use as your separation date. Most couples can agree on a year/month when they both felt the emotional shift from togetherness to separateness. Some situations where living separate is used to help a couple can be:
1) as a step to mend the marriage;
2) as a trial separation;
3) for medical reasons;
4) as the first step in separation while negotiating separation issues;
5) as a first step in separation while working on financial issues.
If we were to write down all the roles and responsibilities and chores that were done by each during the "separate and apart" phase, there would be many configurations, so there is no concrete template for this definition. However, at this stage what is a common denominator is the resounding sensation that the marriage is over and the next step is making a connection with someone to help them with their separation agreement.
Final Word: Most couples who wish an amicable divorce continue to live together in the same house while the issues of the separation are resolved, the separation agreement completed and the items of the separation agreement executed.