From my experience I have seen this appear OOB in Discovery, and only on certain logical CI classes like IP Addresses and such. The use is generally to account for the things that were discovered on a previous scan, but did not appear on the current scan. So the Absent status is a transient status, useful for determining at a later point what a previous configuration might have looked like, but usually those Absent CIs are hidden and may never be reactivated. A later clean-up job (or Data Manager Policy) can be created to clean these up after a time if there is not an existing job to do so. I have in some cases customized a transform map in an SGC where applicable to specifically denote that an expected item was not found. But I have not seen anyone other than Discovery do this OOB.
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