What exactly is NSBundle useful for - only to access resources of the .app package?

...or could I also get an NSBundle that represents the Documents directory, to easily access conte开发者_开发问答nts in there?

I think on iOS it's really only useful for things in the .app package. It originates in OS X where you can load other bundles as plugins, in which case you use NSBundle instances to access resources from the plugin.