[Zubersoft]

The problem is that older devices don't support the "Hide the Navigation Bar" option. That was only added in KitKat. So for these users, the full screen option is the only way to hide the status bar at the top of the screen. Due to the way the immersive mode works, I don't think it's very desirable on the library screen, as having access to the back button is important. Many people (myself included) do want to hide the status bar though at all times. While it's a tad confusing, i do think it makes sense to have both options.