It's one less thing you have to do before you can get on with riding. If you want to drive, you put your key in the ignition and go. If you're cycling, you need special shorts, a water bottle, a lock, check your tire pressure, pull it down from the rack in your garage, get your helmet... the list can go on.

Or, have a beater sitting outside with 60psi, forget the helmet, wear your jeans and just get on with it. The longer distance you ride, the more extraneous stuff become necessary, but it's still nice to avoid it if you can.