I once used Vimium and some bug caused the extension to permanently close my hard-earned ~500 tab collection. So while I feel like I lost a lot, I've never felt so much at peace since either.
is this some kind of modern-day hoarding? how would you even find that useful? why don't you use bookmarks for the earliest ones?
Main reason for keeping tags are they are a constant reminder of topics to look into. Kinda like postits on your monitor. If I put them away using bookmarks I often forget about them and neder get to them. I have folders with hundreds of links I wanted to look a year back and still haven't.
I do clean out tabs occasionally when I am done with a topic but I mostly only bookmark when having to shutdown the system.