What is the origin of the idiom "leave someone at the altar" and when to use it?

The phrase "leave someone at the altar" is derived from the traditional wedding ceremony where the couple exchanges vows and gets married. The "altar" refers to the elevated platform or area in a church or wedding venue where the marriage ceremony takes place. The phrase specifically refers to a situation where one partner, usually the groom, fails to appear or backs out of the wedding ceremony, leaving the other person alone at the altar.