It's a way to quickly add an open tab you intend to read later to an easily accessed folder made solely for that purpose from a constantly accessible button in the URL bar, next to the bookmark button, or the right click menu. I use it a lot for reading manga, news articles, forum posts, and even shows. The Chrome version will even show how long ago it was added to the reading list. It's also very nice when you have periodicals like sites/stories/whatever and don't want to miss them. Its description makes it seem less practical than it is. I'm not even OP but was hoping someone else had posted a solution.