How important is sentry_eventtag model?

This one table grew to nearly 120GB, and a lot of data seems to be rows that got missed out in the routine sentry cleanup command result. How much of a problem is it going to be if I truncate the entire table?

I did run this on a backup machine, and the tags do still show up on events, and so I’m not entirely clear on what part changes when this table data gets deleted.

You’ll want to make sure you’re running sentry cleanup:

Also though, note that PostgreSQL table disk usage will not be freed up when records are cleaned up until the table has been run through a VACUUM FULL. This isn’t run in normal operations for PG. As I recently learned about this myself, you may want to look into using pg_repack in order to vacuum your tables while keeping Sentry online:
http://reorg.github.io/pg_repack/

IIIRC only for indexing of events. If you cleared it you’d lose a bunch of search abilities but otherwise nothing catastrophic.