I recently found out, the hard way, that discovery profiles will get purged from your database periodically. You can set this retention period in your Polling settings, but only to a maximum of 365 days. Its unclear from discussions whether this is a hard limit or if it only gets triggered if you don't use it during the period.
Either way, I would like the ability to flag a discovery profile as permanent, or "DO NOT DELETE" or something like that. For those of us that periodically run discoveries to pick up new items, this is ESSENTIAL for operations. There are just some discovery profiles that should never go way and having such an option will reflect that!!