Imagine a collection of separate, independent desktop work environments, each tailored by you to include the windows you need. Imagine also that you can quickly and easily switch between each of these environments, leaving the windows in all the other environments unchanged.
Think of all the time you would save using these environments, instead of searching through all your open applications and files for the one you need.
VUEMan/2 provides these environments, and calls them Workspaces.