Because somebody (not necessarily you) wrote the following code: printf("%s - %s", id0, id1) You can even do this: printf("user-id %s group-id %s", group-id,

Because somebody (not necessarily you) wrote the following code: printf("%s - %s", id0, id1) You can even do this: printf("user-id %s group-id %s", group-id, user-id) Do you think you will be able to quickly debug what is wrong in a high severity situation when a customer facing system is down? I do not, so we use eids (external ids) that are easy to identify.