Volume Button Assistant App helps you if your phone's -

1. Volume Button is broken.
2. Volume Button not working.
3. Volume Button is hard to press every time.

And by using this App your phone's volume button will have a longer life as well, because you don't have to press it every time.

You can change the volume without opening the app, from the notification bar while -
1. Watching a Video
2. Listening to Music
3. In a Call etc.

You can also use the volume controller after opening the app.