This might be most useful for those who are building their demo labs when you try to nested environment or simulate your disk as Flash when it is actually magnetic disk (MD).
It is also applicable where your Flash Disk/SSD is detected as a normal MD but you need to mark is as Flash disk or revert it when needed.
This is typically very true in a Virtual SAN (VSAN) environment. When you need for a disk group with a minimum of at least one SSD.
If you refer to our KB, you might have to go through a list of commands. However in vSphere 6.0, the web client has the function to do it via the GUI.
Below is a screenshot taken from my home lab. My ESXi server has a normal SATA disk and a SSD disk. So upon selecting either of them the icon will change to allow you to change it. Technically you can even build a all Flash VSAN without having to own a VSAN license only different is the read and write ratio remain the same unlike a real All-Flash VSAN where 100% write goes to the cache disk and 100% read comes from the persistent disks.