If you've just created a new Stack Overflow account, the main feed contains all the available questions: there's no filter applied on it. Then, you can add your Favorite Tags and your Ignored Tags. Since I find the feed is particularly accurate and well filtered, I wonder:
1) How do the favorite tags influence the feed?
I would have said that when the first favorite tag has been entered, only questions that are linked to that tag get displayed, but it would have been too restrictive. The idea is not "the more you tag the more you see" but rather "the more you tag the less you see". In other words, if there are 100 questions at the beginning:
- what should not be: 1 tag > 10 questions, 2 tags > 20 questions...
- what should be: 1 tag > 90 questions, 2 tags > 80 questions...
Stack Overflow implemented it the right way: there are still displayed questions that aren't tagged with any of my favorite tags, but these questions are (usually) still interesting to me. How do they get chosen? Why these ones and not others? Are there relations between tags (i.e. not only synonyms but also linked tags)? If yes, how are they set? Collaboratively or by an admin (or both)?
2) How do the ignored tags influence the feed?
It seems to be more understandable, since you could think that questions tagged with any of the tags I ignored won't be ever displayed. But once again, I already saw displayed questions that were tagged with one of my ignored tags. Why? How have they been chosen?
3) What choice has been made when a question is tagged with a favorite tag AND an ignored tag?
Does the question get displayed or not? It seems also that it depends on criteria, but which ones?