If used as a single source of truth, the DBMS should store true propositions about the world, and that generally means that events are recorded as happening in

If used as a single source of truth, the DBMS should store true propositions about the world, and that generally means that events are recorded as happening in the correct time zone. Also, datetimes that predict forward or recall back far enough may be a case where a timezone is incorrect. The deciding factor is whether you're able to make a true statement. If you're using a DBMS as a dumb data container, and there are plenty of good reasons to do so, then it may also make sense not to use timezones. If you're doing intermediate calculations or sharing with systems that don't support timezones, those values often shouldn't have timezones. That's also why all datetime libraries support times sans timezone.