The comment from homie is based on a misunderstanding. This isn't about showing or hiding unread posts in a feed; it's about showing or hiding folders and feeds (on the left side) that have unread posts. This is useful if, for example, I want to go back to an (unstarred) article in one of my feeds after I've read all the articles in that feed. It's also especially useful since as far as I can see the only way to assign a feed to a folder is to drag it into that folder on the left side — so if I subscribe to a new feed, I can't put it into a folder that has unread items in it unless I go through the rigamarole of opening up the settings page and changing the setting, then putting the feed in the folder, then re-opening the settings page to change the setting back.
The comment from homie is based on a misunderstanding. This isn't about showing or hiding unread posts in a feed; it's about showing or hiding folders and feeds (on the left side) that have unread posts. This is useful if, for example, I want to go back to an (unstarred) article in one of my feeds after I've read all the articles in that feed. It's also especially useful since as far as I can see the only way to assign a feed to a folder is to drag it into that folder on the left side — so if I subscribe to a new feed, I can't put it into a folder that has unread items in it unless I go through the rigamarole of opening up the settings page and changing the setting, then putting the feed in the folder, then re-opening the settings page to change the setting back.