You can disable logging in the admin as well as in `local.xml` so writing to the DB is completely stopped. See this for more info: http://www.axertion.com/tutorials/2012/12/how-to-disable-magento-logging-to-the-database/ . I know some large-volume sites that have logging disabled completely.

Is there any reason, other than being the admin's reference, to keep any logging (`log_*` and/or `report_*` data) at all?