This is one area where Apple falls down. No one who downloads and installs this app would ever be confused about volume vs. shutter button. Apple is just plain wrong here. In fact Apple should have built in the ability to use a volume button as a shutter release.
I can see why it would be useful to have a physical shutter for taking pictures and who really uses the volume control while taking pictures and there is always the software control...then a game company would decide that it would be great to have a physical controller as part of their game because nobody is going to be listening to music while playing their game, so they just add a software volume control inside there setting view...then an art program decides it would be great to be able to adjust brush size or texture using a physical control...then a to do list app decides to scroll its list using the button so the user doesn't have to touch the screen, then a GPS app allows skips to the next turn in the direction list, then a fart app decides to map the button for
😱 [I don't want to even think about that]
The result is that pretty soon the user has no way to know when its a volume control and when the app has retasked it as a programable button and the only 100% reliable way to adjust your music/sound is to use the software control and all of a sudden the iPhone/iPod Touch/iPad are no longer a decent music players since there is no standard way to just directly adjust the volume.
Of course, Apple could arbitrarily decide which apps were allowed to map the button and which were not, that would make everybody happy since their choices would always please everybody.
Its a volume control, if a user wants to adjust their sound level they can do it 100% of the time without having to touch the screen, developers need to respect that. Some people will like it, some won't, and there are situations where there seems to be good cases to remap it, but there is a logic to what Apple is doing.
Note: By changing the switch on the iPad to be a volume control Apple has established consistency across its iStuff again.