Vacuum also shouldn’t be needed 
Postgresql has auto vacuum on by default, which should be enough. I already have a PR where I explain this a bit better in the docs, but it isn’t merged yet #427 - Allow the prune_objects task to delete orphaned activities - akkoma - Akkoma Development
The only task I personally run regularly is MIX_ENV=prod mix pleroma.database prune_objects --keep-threads --prune-orphaned-activities (the last option is also part of the PR I linked, so not yet merged). This removed old posts and activities without local interaction and without breaking threads. I helps keeps the database smaller by removing posts I consider less relevant. Some people prefer to keep all posts, though, so whether this is worth running is really a personal preference.