non legal separation
Question Details: what are the pros and cons
In my opinion, there aren't any real advantages to simply moving out, without starting the legal proceedings for a legal separation or a divorce, except that you don't have the relatively minor expense and inconvenience of the proceedings themselves.
If you are working, the filing fee for a divorce is usually much less than what you have to pay extra in taxes, each year, for filing as married-filing-separately compared to a single taxpayer.
Obviously, you can't remarry if you aren't divorced. And if you wait to get divorced, it can be hard to find your spouse, which complicates matters.
Without at least a legal separation, if your life changes for the better -- a new job with better pay, a winning lottery ticket -- there is always the chance that your spouse will show up, and then he or she will be looking for a piece of the action to go away again.
There are very few pros to a non-formal separation unless the main objective is to merely give each other some space to work on the relationship or see if things improve while apart. The problem in merely separating is that without an agreement in place, you may be held responsible for marital expenses regarding the marital residence, credit cards, car loans etc. Additionally, any promises that may be made regarding payment of bills, support or visitation of children etc., have no legal teeth and you would have to file a proceeding if you wnated these things addressed. Also in New York, you can not receive back child support or maintenance unless you specifically ask for it in court or have a written separation agreement. Thirdly, if you have a pension or other retirment fund, merely separating does not stop your spouse's entitlement to that. You would need to file for divorce or file a separation agreement.
Basically you are on an honor system when you separate without some formal documentation and you may place yourself at a disadvantage by leaving. Obviosuly if the situation is volatile and safety is an issue, then you may not have a choice to leave first and deal with the formalties later. Absent that, think long and hard before merely leaving.