Depends what app you're in. For some, that will change the system volume, but for others, only that app's volume. (There are obvious advantages both ways, but that's irrelevant.) If you're using one that doesn't affect the system volume, then you'll want to adjust the system volume from the tray for, e.g., going between speakers and earphones. Let alone if you have your media player in the background and something else up -- the status bar should be more convenient than switching apps twice. (Although if one can't reliably actuate it with fingers, it may not be; it works fine for me, though.)