This is as much common courtesy as anything else, but, it’s disheartening how few people abide by the rule.
Really, it applies for everything: movie theatre seats, the bus, lineups. The more cramped you are, the harder it is to look cool. It’s all about perspective. You want to allow others a certain amount of distance so that they can properly take you in.
Remember, it’s the space in between where the magic really happens.