@thatbrickster Whoa, I thought that my local database of 250 Mb is the largest used with #AndStatus. It looks like you configured AndStatus not to purge old notes in Settings -> Storage?! Please do this if you see that the database is too large.
Your own notes, reposts and likes by you shouldn't be purged in any case... but I would create a backup first...
Regarding treating local database as a cache: cache is what can be re-read from a server, if necessary, but if you store data for years, like I do, you have in your local database content that may be unavailable at the original source. Or that source server may be already shut down... Moreover, I see posts telling that e.g. a timeline from #Mastodon is available for several _days_ only.