TBRSS has fewer features than other feed readers: this is by design, because most of those “features” implicitly benefit the operators of the feed reader at the cost of its users, by promoting compulsive behavior.
I used to think that tagging (or categorizing, or labeling) feeds was one such misfeature.
The heart of TBRSS is the reading list. However many feeds you subscribe to, when you log into TBRSS what you see is a reading list of the 10 entries most worth reading.
I think of that 10 as very optimistic. It would be remarkable for ten things worth reading at all, let alone ten things worth reading for any particular person, to be published in the same few days.
Separate reading lists for separate tags, I thought, would just surface more noise. And tags, in particular, are problematic: they offload to the user distinctions of relevance and quality that should be made by the code itself.
But that view is idealized. The fact is, we all have areas of special interest where our standards are relatively low. Running a website, I need to keep up with certain technologies, and to do that I need to keep up with certain sources and authors, even if they fail to crack the top ten. (Every time I visit Hacker News, that’s a bug.)
Besides that, there was another consideration: I wanted to make sure that the OPML file you download from TBRSS is reasonably close to the OPML file you upload – and since that means internal support for tags, it might as well become a feature.