Derived house is very interest and extremely important which we use the same thing in Chinese System as well. One chart shows all the people and matters around one's life. It is through the derived houses you can see your grandparents, and relatives so as everything else in your life.
The relationship of 6th house, as an experiment, I mentioned in the other thread, taking 6th house as the first, 3rd of 6th is 8th house, then 10th would be 5th what 6th house loves and fantasized, status, recognition, authority over others to do that, 6th house will have to learn to sacrifice oneself 12th house, 7th of 6th to achieve the goal.
The original 1st house became the 8th house of 6th, we are in debt to the 6th, or the 6th house is in debt to us? Interesting.
The philosophy of work or philosophy of service and health, will have 2nd house as the 9th, at the end both Wealth and Health are similar, our own possession. While the original 9th house is the home of 6th, perhaps our daily works is built upon the foundation of our high mind and believe system etc.
At last, 5th house will be the 12th house of 6th, when you have too much fun, the 6th house will suffer for health, work, daily tasks will be disordered.
Edited: I don't think anything had changed very much in today's world. One interesting thing though because of the class system, slaves for generations will not be able to climb up to 10th house no matter how much they fancy that status (in the past they do treat their masters as God, in Egypt particularly). These days, we have a little more chance to research that status but yet a master is a slave to something else higher than himself and indeed depending on his slaves to survive.