It's more akin to an extra monitor with all the icons & menus duplicated than an additional user. It isn't meant to be independent - the aim is to give you more workspace.
I've used it on Linux for a long time to group windows for particular tasks - browser and e-mail on one desktop, word processor & such on another, graphics or photo program on a third and miscellaneous on a fourth. Another thing I do is have video running on a second monitor with the video window on every desktop so I can switch desktops and keep watching without interruption.