There are nice explanation and examples here – https://stackoverflow.com/questions/5876218/difference-between-timestamps-with-without-time-zone-in-postgresql
…but long story short, I would not bother at all. In the end Postgres does the shifting between timezones and do you really want one more moving piece? I don’t. You’ll then have to take this into account when loading those from the DB in your app code and that’s prone to ambiguous rules (f.ex. I lost count on how many times I had to convert DateTime to NaiveDateTime in my Elixir work to avoid confusion). For years now, I store all timestamps without timezone and in UTC from all Elixir / Golang / Rust code that I write, and I leave showing the time in local timezones to clients (websites and mobile apps).
And I’ve made friends with frontend devs and sysadmins by never doing any shenanigans with timezones as well. 
Finally, storing future datetimes can sadly be error-prone; we don’t know when will a timezone change offset or eliminate / add summer time shifting. I forgot where that discussion was here on ElixirForum but I believe @LostKobrakai was in there and I think Ben as well.
