A legal separation requires all of the same legal steps as a dissolution of marriage (divorce), including residence, grounds, pleadings, and court appearances. The only difference is that when the decree is rendered, the parties are "legally separated" rather than "divorced" and are, therefore, not free to remarry. Unless there is an order or agreement to the contrary, rights of inheritance and the duty to support may remain.
A legal separation may be changed to a dissolution of marriage (divorce) by either party asking for a dissolution at any time, unless they have filed a declaration that they have resumed their marital relations.
Married couples who wish to do so may separate, and live apart, without court permission. The benefit of a court-ordered separation is that the court will establish responsibilities for alimony, support, custody, etc., eliminating uncertainty.
A separation agreement signed by the parties will have many of the legal implications of a court-ordered "legal separation." Such an agreement should only be entered into with advice of counsel.