In some divorce actions, one distribution of property. For example, he may not wish to share his pension.
The absence of outside common law marriage.
Sometimes when a couple marry as a spouse (usually the wife) with the problem of proving that it did. She must establish to a court’s satisfaction that she and her husband presented themselves to the world as a married couple.
Obviously, a marriage certificate would have made it easier.
Protocols vary with jurisdictions, but normally a clergyman or official returns the marriage license to a county where the marriage happened and a certification is mailed in a few days.
See also Common Law Marriage.