For example, interesting finds when developing plugins or mods using the vanilla system (spigot, forge, etc).
Just wondering, because this wiki reminded me of the interesting finds I had when I added custom enchantments to the game at runtime with Spigot. Whenever the server is reloaded, all custom enchantments are removed from items and have to be re-added. This will not be the case with forge, but just thought it was an interesting find.
Edit: This was also using the vanilla code and not Spigot. It just so happens that I was using a Spigot server and plugin to add the code into vanilla (e.g. vanilla thought there was more than the normal amount of enchantments. You cannot do this with Spigot normally).