The primary role of the optician is to bring money into a store. We do this by selling optical products. Optical products can be thought of as anything above-and-beyond the frame and the most basic CR-39 lens. This includes all lens add-ons and accessories.
Lens treatments are like cars.
I may drive a basic Toyota Corolla, but would prefer a loaded Nissan Altima, yet really want a Ferrari!
You can sell a very basic pair of glasses which will work well and be reliable (a Corolla). You can also sell a basic pair of glasses and begin to add on features to make it a better pair (an Altima). Finally, you can sell the highest end products with every possible add-on (a Ferrari).