Read OP's post please. They're talking of systems where it was acceptable to always do full table scans, in one case having 350 rows. Not "an incredibly expens

Read OP's post please. They're talking of systems where it was acceptable to always do full table scans, in one case having 350 rows. Not "an incredibly expensive task on a dataset so big that it needs one". Thus I read OP's post as recommending to not do premature optimization (without using those words literally).