As far as I know, and correct me if I'm wrong, if you hit the Home or Back button after using apps such as Music for example, as long as it doesn't require an automatic update at a certain interval or use any system resource such as GPS location, it just sits in the background and doesn't use any resources until the OS deems it necessary to kill the process.
Using Music for example, if you pause the music that's playing and hit home, the process just sits in the background not doing anything. After using PC's for many years, I did have to get used to not having to necessarily close an app after use...but I did get used to it after a while.
Using apps such as Navigation or other ones that require a data connection or GPS services I make sure are closed out fully or they usually have a disconnect or exit option.