Using a virtual desktop manager is a way to organize applications over several virtual desktops. For example if you use two virtual desktops you can put a webbrowser on desk 1 and by using a desktop manager switch away the webbrowser and it will seem like you have a new empty workspace (desk 2) to put another application/applications on. Virtual desktops are very common in the Unix community and once getting used to this, it is very hard to manage without it.