I was curious myself, and i didnt like any of the other answer because they didnt seem to answer what i was looking for atleast.
Looking back at this doc it almost appears as if Thomas was stating is giving it another dedicated ip on the loopback allows it to be canonical.
Both point to your loopback. Using the following
is an actual IP, on the loopback, whereas
is either the device itself, or another ip on the loopback. Both end up on the same subnet, representing the loopback, but are separated by ip.
They are equivalent dns wise, but separated because of having dedicated ip.
The point being, you can have all your entries on one line like this
127.0.0.1 localhost localhost.domain www.myfakednsname.com myakednsname.com
If your hostname is local, meaning doesn't have a global internet DNS entry mapped to an actual internet ip, then in this case Thomas was saying you NEED TO have the 2nd entry line, like this to dedicate it there (to canonical).
127.0.0.1 localhost localhost.localdomain