networking - difference between local and inet socket?

I noticed that, while setting up opendkim, the options for the Socket are:

#SOCKET="local:/var/run/opendkim/opendkim.sock" # default
#SOCKET="inet:54321" # listen on all interfaces on port 54321

#SOCKET="inet:12345@localhost" # listen on loopback on port 12345
#SOCKET="inet:12345@192.0.2.1" # listen on 192.0.2.1 on port 12345

What is the difference (if any) between the local:[...].sock socket and the inet:[...]@localhost socket? Do user permissions come into play for one or the other? Is there a security benefit from using one or the other? Are there any functional differences at all?