If there was only one, that would the one described on the picture below depicting a desktop lifecycle. Simplifying lifecycle!
Traditionally, you must procure, image, secure, deploy and then monitor, maintain, back up and retire your physical desktops.
With VDI, you only need to generate the original image by creating a reference computer, use it as the core image for all systems, personalize it and then monitor and update it.
For the other advantages of VDI, read the full article at Techtarget.com