This is the place where you come to customize the Share Charm. You can customize the applications that can be used by the Share Charm, the order of the apps in the charm list, clear history, etc.
The first two options customize the order of the apps shown in the Share Charm pane. If you turn them on, then the apps that have been used the most for sharing will be listed at the top. If they are turned off, then the list will be shown in alphabetical order.
You can also specify the maximum number of apps that can be shown in the list. This is useful when you have too many metro apps installed, and you want to remove the clutter.
Other than that, each metro app is listed in this section so that you can specify whether or not the app is available for sharing. I have turned off People apps for sharing. So it is not seen in my Share Charm pane for sharing.