From what I know, the idea behind this is to simplify posting.
Having tags instead of categories may complicate posting - instead of choosing just one category, users will have to decide whether a tag is good or not for their post - for every tag separately, which is a real rigmarole.
Instead of tagging, the focus is on two things:
- What is hot / new right now
- The search function.
Actually, if you have an excellent search function - and it just works - then you don’t need tags. And now this makes readers’ lives easier, not only writiers’ ones - because now readers do not have to find out which tags will possible contain a post which they want to read.
To better understand the issue with heavy categorization or tagging, consider movies discussion forum.
One cannot disagree that there are many movies which belong to many different categories.
What is more, while for one a particular movie can be hilarious, for someone else it can be not. So putting such a movie under
hilarious tag will confuse those for whom it is not such a move.
Now consider you don’t have that
hilarious tag / category.
So a curious person would just use the
Search button and will see only those movies where hilarious is mentioned most of times, with most likes etc etc, which means more than one people considered the movie to be hilarious.
As you can see, getting rid of categories/tags and focusing on better search and
what's hot right now makes the quality of your content higher in the eyes of your users, and confuses people less, and as a bonus you simplify posting, so no one has to break their head thinking about how to categorize/tag their new topic.
Hope this makes sense for you.