There is a way to show the "Desktop", "All Active Windows" and "Workspace Switcher" by just hovering ur mouse to the edges of the screen.
One way this can be done is using "Ubuntu Tweak".
The four corners of the desktop can be made put into use effectively by using to them "Show The Desktop" or as a "Workspace Switcher" or to "Show Active Windows". Something like the Gnome 3's top left corner.
I have done this on Unity and I don't know about the same working on Gnome 3.x.
Here's How, Install Ubuntu Tweak, execute the following Commands
Once installed, please proceed to "Tweaks > Compiz Settings", under "Compiz Settings" configure the edges of ur screen to ur desired functionality.
Now u don't even need to click anything. Just touch the edges. :)
Install Ubuntu Tweak. Here's How,
Go To Software Center,
and add the following PPA to your Software Sources
Close out and go back into Software Center. Search and install "Ubuntu Tweak".
Now make the changes as shown in the screenshot.