Hello Ganimede,
just to add to the previous (correct) answers: the first example which comes to my mind is archiving.
For example: SAP gives you tools to archive invoices, lists, etc.
So if you open an archived document later (e.g. due to end-year duties), and need further information, you can not see the responsible behind the archive, because ABAP user details have been deleted.
Of course, HR could give information who / where was working during the time *that* document has been archived, but what is an integrated ERP software good for if data are missing and you have to look around in other departments?
Other than that, inconsistency really should be avoided.
Best regards,
Laszlo