Being a post inspired by someone's wondering how, in a SF setting, two couples got married. Apparently under the impression that you needed someone to do the ceremony.
In later medieval Europe, you didn't need someone. If the man and the woman exchanged the words of marriage, even alone and without witnesses, they were well and truly married. True, it led to a lot of awkwardness, which is why requirements for witnesses were added, but in a SF society, you could just register it on whatever computer system did it, and have it over with.
Not exactly unusual. There are no doubt few cultures where festivities are not normal at a wedding, but the formalities can easily be few. A Chinese woman enrolled in her husband's family book is married, which is why we had contrempts in the 19th century about whether they could come to the Americas to husbands they had never met. Though European women going off to foreign lands as brides sometimes did so only after a marriage by proxy, which would give them better legal protections than a betrothal, even in the days when betrothals had some teeth in them.
There are a lot of ceremonies, too. In early medieval Europe, before the Church managed to insist on the vows thing, the wedding ceremonies -- among those rich enough to bother -- consisted of drawing up the legal agreement, something to which neither the bride nor the bridegroom needed to be party, and then a rather ribald escorting of the bride and bridegroom to bed, perhaps many years after the agreement was made. Religious ceremonies may consist not of vows but of paying respects to or even making offering to the suitable god. The bride may escorted from her parents' home to her husband's -- or her in-laws' -- and thus be married.
Lots of possibilities.