Unfortunately, my colleagues and me had the displeasure to look at that distinction between timestamp and timestamptz in Postgres very deeply. All that is written above is correct from my understanding, but it is not the complete picture. Even in the case of a column of type `TIMESTAMP WITHOUT TIME ZONE`, the Postgresql JDBC driver may convert time to UTC if your session time zone is not UTC. I write "may" because it depends on whether the binary protocol or the text base protocol is used and that depends on whether prepared statements are actually used between the Postgres client library and the server.

We had the requirement to store dates and times coming it without changing them at all cost, but still using the space efficient epoch format. And we didn't know the time zone of the time when we had to store it.