I’m not seeing the great insight here. From my reading, it sounds like the author is saying something akin to; when performing some IO task like fetching line i

I’m not seeing the great insight here. From my reading, it sounds like the author is saying something akin to; when performing some IO task like fetching line items from an order it is better to fetch all the line items at once related to the order than it is to fetch the order and then fetching each of its related line items in a loop. Incidentally, this is why I advocate for SQL in application code or the use of stored procedures. If I had a nickel for every time I’ve seen the latter example when ORMs were used.