The ONLY difference between a legal separation and a divorce (marital dissolution) in CA is that, at the end of a legal separation you are not free to remarry (or enter into a domestic partnership) and at the end of a divorce you are. All the other aspects of the divorce process are the same in a legal separation. That should not be confused with having a "date of separation," which is a measuring point for certain rights and responsibilities, it is not a "legal status," as having a judgment of marital dissolution or having a judgment of legal separation would be.
Almost none. All the same issues (custody, visitation, support, property division and debt allocation, etc) are all resolved in a Legal Separation just the same as with Dissolution. The only difference is that at the end of a Legal Separation proceeding ... you are still married. That said, it is very easy to go back later and dissolve your marriage.
One additional difference that I might add is that you don't have the jurisdictional requirement of residency for 6 months prior to filing for legal separation, so it is often used to get interim support and custody orders; also, while divorce can be obtained after a legal separation, it is best to check 'both boxes' on your original Petition (one for Dissolution and one for Legal Separation) so that you can come back later in the same case; otherwise, you have to refile.
Many people choose a legal separation over divorce for religious reasons. Property division, custody and support issues can be addressed in both a legal separation and a divorce. At the conclusion of a divorce you are free to remarry whereas at the end of a legal separation you may not.
One additional reason why some people choose legal separation over dissolution is to preserve the marital status for health insurance entitlement purposes. If a person is covered under a spouse's health plan but might not be able to qualify for insurance on their own or could not afford insurance on their own, preserving the marital status could entitle them to continued coverage on the estranged spouse's policy.
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