I recently had to call the help desk to have an issue sorted out on my corporate workstation (Windows 7) and as I was sitting there I kept thinking to myself: "Now wouldn't it be great if I could set aside my second monitor as another seat?"
Think about this. You're working on some big project or preparing for a new project that isn't properly planned or just needs to be completed quickly, and you need some new set of software or permissions for some set of workgroup and then reality sets in. This is going to require three calls to tech support over the next week.
What an unnecessary frustration. If only this one computer could be used by two people simultaneously at the same time!
So it may not be a very common occurrence but it certainly seems to happen at the absolute worst times. Help desk just has to take over your computer remotely while you sit there and watch the mouse move and talk to the person on the other line.
There are a lot of practical uses for having multi-seat capability, even if you are on a computer that you intend to be a permanently single-seat workstation. There are always those random times here and there where a second person might need access simultaneously.
Now I just wish I had a Linux workstation at work!