It's a tad bit more convenient and it doesn't really hurt anyone else currently. That's one good reason. It's nice to be able to sit down and not have to wait those few extra seconds to log in just like it's nice to have a computer that boots up in 15 seconds instead of 30.

But even if there isn't a a good reason, why does it matter? It's what people want to do. If they aren't hurting anyone else in the process, leave them alone.