From a user point of view I prefer to have the option to either specify how often to check for updates, as well as disabling the check altogether.
One particularly annoying example of a program that didn't let you do that: Skype 2.0 kept bugging me each time I started it that there was a version 2.5 available, and tried to get me to download it.
Very convenient, except 2.5 didn't work with my webcam so upgrading to that version essentially made the entire program worthless to me.
(the newer 2.6 Beta does work again, and now it finally has an option to not automatically check for updates as well)
Since not every upgrade is necessarily 'better', it's nice to have the option of just sticking with what you currently have.
One particularly annoying example of a program that didn't let you do that: Skype 2.0 kept bugging me each time I started it that there was a version 2.5 available, and tried to get me to download it.
Very convenient, except 2.5 didn't work with my webcam so upgrading to that version essentially made the entire program worthless to me.
(the newer 2.6 Beta does work again, and now it finally has an option to not automatically check for updates as well)
Since not every upgrade is necessarily 'better', it's nice to have the option of just sticking with what you currently have.