I know, it is the Current Year, you don't need to worry about disk space. Until you do! Via a comment on this article I found this to purge a bunch of old log entries (on my personal machines I don't care about anything more than a day old, tweak according to your situation):

$ sudo journalctl --vacuum-time=1d
[literally six million lines of text]
Vacuuming done, freed 616.1M of archived journals from /var/log/journal/8ab90b50ecb94b5ba09cacf15a486a8e

Yay!