Its constant drain even when not 'in use' seems to imply it's classifying tabs as they change page (though it might be telemetry or uncommented testing). If so, it's an example of premature optimisation gone very wrong.
It's a shame, because it overshadows the fact that naming tab groups is a perfect use case for an LLM, alongside keyboard suggestions and reverse dictionaries [1]. I'm ardently distrustful of LLMs for many, many purposes, but for the tiny parameter and token usage needed it's hard to not like. Which is a shame it's (somehow) such a drain.
[0] https://github.com/mozilla-firefox/firefox/blob/7b42e629fdef... exports a SmartTabGroupingManager, though how or why that is used without being asked eludes me
[1] https://www.onelook.com/thesaurus/ Can be helpful in a pinch when a word's on the tip of your tongue, though its synonyms aren't always perfect.