>>I realize now that my application is very simple. I have hundreds of SQL Select in my application and for the most part they are so simple that the question of either sub-query or CTE does not even come up.
>>I know I should return all the money I have gotten from the customers over the years but I have already spent them :)

I find that customers seem more interested in features than everything under the hood, while I'm mostly impressed by robustness and code that has survived decades so far by not relying on specific version or Rube Goldberg cleverness du jour... such as the clarity and reliability of simple queries. If and when you have a gap in paying work or if some parts could do with better performance, you might revisit to consider replacing several queries with subqueries or CTE - otherwise it ain't broke and doesn't need to be fixed!