This convention ensures that you have a way of uninstalling most of the contents of your datapack. The word "most" is used here because Minecraft does not provide the necessary tools for us to actually uninstall or remove the entirety of the datapack.
There are no rules enforcing how you should implement the uninstallation method, as long as you do implement it. However, the following section outlines one of the many ways to implement it.
You can create an "uninstallation function", which when ran, will remove most of the content added from your datapack. You can tell the user about this function inside your project page or anywhere you like.