Reason to use; nvm mainly used in Mac/linux environment, but not in windows, and nvm-windows just do exactly this (for windows)
Some of the project requires later Node version, while some only worked with older version. That's why we need a node version switcher to toggle between the 2. Here's how to configure it.
Head on here to for nvm-windows README.md here https://github.com/coreybutler/nvm-windows/blob/master/README.md