@Lotus If you are not subscribed to an image or a thread and post there, or are uploading a new image/thread, you will get subscribed to it automatically.
In Booru-on-Rails, this was three separate settings options (subscribe on reply — comments and posts, subscribe on upload — images, and subscribe on new threads — threads) in their own tab in settings, and users could opt to not have autosubscription happen. It was not ported to Philomena and for whatever reason it was defaulted to option that causes more actions (you need to subscribe once, you need to UNsubscribe every time).