Disables the plugin update checking and notification system.
Most people will not want to (and should not) disable this feature. It's a fantastic feature WordPress and I'm fully in support of it. However, administrators who maintain multiple installations of WordPress on behalf of other people (eg. clients) may not want plugin update notifications to be shown to the users of these installations. This plugin is for them.
Yes. Please see the Disable WordPress Core Update plugin.
Yes. Please see the Disable WordPress Theme Updates plugin.