I just find with two or more people there’s more to keep in mind for orders and stuff and remembering what kind of drinks someone has for topping up or refilling, plus the cooks (should) get a portion of the tip so they’ll be cooking twice as much food at the same time which is a little more difficult. In general it’s a little more work to serve more people because of time constraints and number of things to remember.
You can have 12 single people at 12 different tables and it would be a lot easier than 24 people paired up at 12 tables.