If you use Ubuntu 16.04 with compiz (gnome-flashback), you will see that you can not use virtual desktops because when you click on it with the right button in the virtual desktop selector to increase the number always returns to have only one again.
sudo apt-get install ccsm vdesk
- Then we run ccsm and select these options:
General ► General options ► Size of the Desktop
(you must press the right arrow to access to this option)
- Now we can increase the horizontal size.