This is to allow torrent creators to provide updates to users. There are two distinct features here: The ability to modify or update a torrent, re-using any already downloaded files and pieces, and the ability to automatically receive these updates. I'll call these features "mutable torrents" and "cascading torrents". An example of mutable torrents might be this: A content creator puts several hundreds or thousands of megabytes of video into a torrent. Then they realize they made a mistake and they want to modify some of the metadata, add a video they forgot, fix subtitle typos, etc. Instead of forcing their audience to download the entire torrent again, they could release a torrent that leverages the fact that many people already have most of the contents downloaded. Then, those that download the torrent would only have to download the parts that have changed, re-using what they already have. If the revised torrent was created with this in mind, this will happen automatically. But some people may find use of that menu item to mutate a torrent manually. An example of cascading torrents might be this: A content creator releases some form of episodic content. Let's say it's a web series and they release a new episode every week. Using the cascading torrents feature, they could embed an "update url" in their torrent that would occasionally check for new episodes. When a new episode is available it will then automatically be downloaded. Hope that cleared things up!