[fleetfox]

With triggers you can fetch and index data from relations.

[joevandyk]

This is the main reason for me. I have to be able to quickly search data that's stored in a couple different tables.

Using an index means the read queries become a little more complex (they have to exactly match the index expression).

[pgaddict]

relation == table

relationship == foreign key

[fleetfox]

Did i phrase it wrong? You can fetch and index data from related tables.

[spoiler]

I think he simply tried to clarify the difference to people who don't understand jargon.