I think what he is trying to say, is that knowing how your database stores and accesses the data, can help you make better decisions in writing SQL statements.

I think what he is trying to say, is that knowing how your database stores and accesses the data, can help you make better decisions in writing SQL statements. The example he gives is that a stored procedure for a large query used to take almost 1GB but now it takes only about 1MB because he is "cooperating" with the way the database slings data around.