[irrational]

It's useful for people new to Postgres, since many of these things are particular to Postgres.

[tempguy9999]

Not really. Most is pretty well standard SQL (CTE optimisation fence pre PG12 being one exception, and there are a couple more, but really it's mostly standard stuff).

[barrkel]

The :: syntax for CAST() is also a psql-ism.

[tejtm]

Maybe that is what it is now, but I still have muscle memory using it in Informix.

[irrational]

Maybe. I come from the Oracle world and the majority of these don't apply to Oracle.