Still very new here, but this is what I've discovered....

If I go into a thread and decide I don't want to see it again or be updated on it, I just use my back button on the browser. If I don't do that, I've discovered that I automatically subscribed - even though I didn't plan to.

Now, if I don't use the back button, I just delete the notifications I receive and ignore the thread if it is in a forum I want to peruse.