As you stated, user accounts come and go. So it's also worth mentioning that numeric values for user and/or group will be displayed if there are not matching entries in /etc/password and /etc/group.
After all, its only for the benefit of "Meatspace" that the numbers need to be mapped to text.
And of course there's the count= option as well. Handy for blowing away partition tables on a drive that has previously been part of a raid array, or are of a format that linux can't recognise.
dd bs=512 if=/dev/zero count=4 of=/dev/sdb
Back in the day, we used to use dd as the output pipe for tar or cpio when backing up to tape. Streaming tapes like a continuous stream of data, and tar, cpio and the like don't do this nicely when there's a lot of small files.
This would cause the tape drive to "shoeshine" the tape heads, as it needed to stop the tape, rewind and get a running start each time the data stream ran dry. (Not good for either the drive or the tapes due to wear and stretching.)
As you stated, user accounts come and go. So it's also worth mentioning that numeric values for user and/or group will be displayed if there are not matching entries in /etc/password and /etc/group.
After all, its only for the benefit of "Meatspace" that the numbers need to be mapped to text.