It meant to be used when you want to disconnect temporarily.
Lets say you are connected to a cafe wifi and want to browse a website but at the moment the wifi is slow or the site has issues with the wifi. At this time, you want to temporarily disconnect from the wifi then do whatever you want to do.
You don’t need to turn it back on. It’ll turn on automatically. You don’t want to realize that you’re using cellular data after you watch 1 hour of a 4k video.