As a rule of thumbs directories should be cleaned up by the owner; how would you know what can or cannot be purged otherwise?

If a specific directory is used for logging purposes that answers your question about why they keep filling up -logs grow, that's what they do best.

What you can do is to set an alarm at 80% or whatever threshold you think it's appropriate and let your monitoring system cut a ticket and page the rightfull owner of the directory.