Hijacks the bottom of the (bottom, if there is such a thing) monitor.
The bottom right corner (and, in the unlikely case where your X server doesn't support pressure barriers, only the corner) toggles the message tray.
The bottom left corner executes, if enabled, a configured command.
By default, the custom command is disabled and can be enabled and changed from the preferences.

The preconfigured command is: xte "keydown Super_L" "key D" "keyup Super_L"
The hint is that the bottom left corner could be used to toggle the display of the desktop.

Of course, for that to work xte should be installed (yum install xautomation).
And, of course, Super+D should be configured to "Hide all normal windows".
("System Settings" > "Keyboard" > "Shortcuts" > "Navigation")