I assume it creates multiple desktops (not workspaces - I know the difference) as the name so pragmatically implies. I set it to 2, and if it does create multiple desktops I cannot figure out how to switch between them. I've googled and checked AskUbuntu.
In the previous version of my answer I mixed up the concepts of viewports and desktops. What I wrote below applies to viewports, not desktops. Desktops don't seem to be supported any more, the setting in CCSM is probably outdated and doesn't do anything useful anymore. I edited my answer accordingly.
There are several ways to switch between viewports:
You can switch between your viewports by a variation of the cursor keys. For example, to go to the viewport that is located to the right of the viewport you currently are on, press
Button in Launcher
There is a button in the Unity launcher (the bar at the left side) that allows you to switch between viewports with your mouse. The symbol shows the 4 viewports (2 x 2) that were standard before Canonical decided that having multiple viewports activated by default was confusing for people. If you click on that button, you get a "bird's eye" view on all your viewports and can simply click on the one you'd like to go to.
Switching between viewports with the keyboard shortcuts or the launcher button are the most common methods, but there are more. I, for example, have activated one of the "active corners" to show the "bird's eye" view described above. So, whenever I move the mouse cursor to the lower right corner of the current viewport, I can switch to another one. You can configure the "active corners" with tweaking tools like Unity Tweak Tool.