Think of buying a new laptop and not having to install anything. All your programs, files, and and settings are in the cloud. The programs open files from your cloud storage, without you having to download them first. So no user files and docs have to be stored on the machine.

Now, if the machine is only used to run such a desktop, then such an internet OS might run best on a chrome-book style device, with minimal storage for system data only, and locked down to run only the internet desktop. You could even store your entire config settings in the cloud, so when you log into the machine, it is automatically configured. So all you need to to acquire the hardware, and you are to use it immediately. No more mucking around with settings and installations and drivers and whatnot.

This setup is not good for every user in every situation, but in some scenarios it would be very useful.