I went to buy tickets to a comedy show last year and they wouldn’t let me buy a single ticket. I had to buy 2. It quite literally doubled the cost, and then a seat went empty.
If someone were to buy 3 tickets, it could just as easily leave an orphaned seat.
I've seen it twice now, both times within the past couple years. I'm not sure if it is the venue of the performer that imposes it, but it's really bad. To get single tickets, people are basically left to sit and wait for all the other seats to be bought, then hope there are single person gaps they can fill.
If someone were to buy 3 tickets, it could just as easily leave an orphaned seat.