I'm not disagreeing, but it also helps to look at the EXPLAIN output (including things like width and rows) for queries to better understand what's actually hap

I'm not disagreeing, but it also helps to look at the EXPLAIN output (including things like width and rows) for queries to better understand what's actually happening. That helps build intuition, but like you said, major version releases can change that behavior. Postgres is usually pretty good at documenting those changes, though.