New clients often do not know the difference between being separated, being legally separated and being divorced.
People who are married and no longer living together are "separated". However, they are not "legally separated". To be legally separated there must either be a properly drafted, signed and witnessed Separation Agreement or a judicial decree determining that the couple is legally separated. Verbal agreements, informal agreements, living apart for 10 years without a proper Separation Agreement or court decree does not change physical separation to legal separation. In almost all cases a properly drafted, signed and witnessed "Settlement Agreement" can also be utilized as a Separation Agreement because the divorce Settlement Agreement also expresses that is the intention and desire of the parties that the Settlement Agreement also constitute a Separation Agreement.
Now that the definitions are clarified the original topic is what is similar and different between the two.
The biggest difference is that with a Separation Agreement the parties are still married, they are not divorced. So therefore neither person can legally marry someone else.
A Separation Agreement can cover all of the same topics as a Divorce Settlement Agreement. Issues of custody, parenting schedules, decision making, child support, spousal support, division of marital assets & debts and determination of separate or pre-marital property can be resolved in the same manner. Additionally, either agreement can provide for waiver of inheritance rights and other waivers of benefits of marriage (even though the divorce has not taken place).
One significant difference is that if a Separation Agreement has not been court ordered or made a part of the divorce decree (this is the simple description) then if one person does not comply while it is a "breach" it is not "contempt of court". Therefore, enforcement of obligations in a Separation Agreement that is not court ordered can become difficult as they are viewed as "contractual" rather than "court ordered". Additionally it will be somewhat easier to seek a modification of an Agreement that is not court ordered. Since the court has not approved the agreement the standards for modification may be less rigorous.
An advantage of a Separation Agreement vs a Divorce is that if the parties were to reconcile they do not have to re-marry as there was never a divorce. Instead they can sign a proper document suspending or terminating the Separation Agreement. If the Agreement was previously court ordered then the suspension or termination will also need to be submitted to the court for signature.
So while many aspects of both concepts are similar there are distinct differences. If you have any doubts as to what is the best choice for your situation it should be discussed with your experienced matrimonial attorney.