Try not to think of it as creating and destroying. I did for a long time until I realized that it was keeping me from putting some of the more advanced stuff together. Let's talk from a TCM point of view first. Try to think of the cycles as a yin cycle and a yang cycle. They work together to try and keep things regulated and balanced in the body's energetic system. This balance is maintained by the eight extrodinary vessels or "strange flows". If you haven't yet, get a book called "The Extrodinary Vessels"[dont remember the author, mine's back in Texas] it is very helpful in this area. The vessles act as a reservior system for the meridians, allowing the excess to drain in and flow out to where the depletion is. This is the two cycle's working together to create a balance in the system.
Now comes kyusho...
Everyone needs to understand that you can use all three cycles to produce effects. Let's look at a destructive(regulatory) series of strikes.
When you grab or strike fire you cause two reactions in the energetic system you cause a depletion of the enery in the metal meridians, and cause an over-abundance of energy in the earth meridians. We must realize that neither of these situations is good for the body. The body always wants the energetic system to be in balance. If you look in some TCM books(or ask the acupuncturist) there are different bad things(symptoms) that happen when there is too much or not enough energy in an organ system.
Kyusho strikes add large quantities of energy to the system, this can cause the natural process of balancing to fall severely behind. Allowing us to take advantage.
The diurnal cycle, is the natural direction flow of the energy through the merdian system.
So you have the cycles working together to keep the body regulated/balanced.