Photographers can often be lumped into two distinct camps. The first is the "what" group which is represented by people who study their craft and follow tutorials as if they are a scripted set of instructions never caring about anything other than if the technique works or not. The second group is the "why" group who study their craft and follow tutorials while also striving to learn about why what they are learning actually works. The second group has a tremendous advantage over the first as their deeper understanding of technique gifts them with far more versatility than those who simply collect a library of preset recipes with little care as to why those recipes work.
"Why" Empowers You To Solve Unexpected Problems
There is never a moment when every aspect of a shoot is perfectly consistent with what you expect. There are always curve balls. If you don't know why a given method or piece of gear works you have virtually no ability to adapt in the face of an adverse problem. Personally, I've encountered this often with other photographers who can create great images so long as the stars stay align, however, as soon as something goes wrong a frantic call comes my way from a panic-stricken photographer hoping that I have the answer to his or her calamity. In almost all cases the owner of the hysterical voice could have easily solved the problem if he or she had taken the time to dig beyond the superficial surface of their learned workflow.
"Why" Allows You To Create New Techniques
The growth of the photography industry has always been driven by those who gravitate towards the "why." By understanding why a formula functions you have the freedom to adjust that formula to either create something different or to function better. One example I like to always use was from a workshop with Joe McNally back near the start of my career. He was shooting at sunset and wanted a beautifully vibrant sky behind the model. Mother nature, however, wasn't cooperating that night. McNally wasn't phased, he instantly had a solution ready to go by digging into his world class knowledge on why light behaves the way it does in different situations. His solution was remarkably simple. He gelled his lights green. At first, I thought he had gone off his rocker. The photos on the back of the camera looked terrible. The sky was still the boring dull blue color while his model turned a sickly green tone. I was unimpressed. That is, until he brought the photo into post and adjusted the tint to return the model to a neutral white balance. Instantly the green went away as magenta was introduced to the scene. Meanwhile, the sky became richly toned with magenta as it didn't have any green to offset. The solution worked wonderfully, simply, and elegantly. McNally's understanding of "why" light behaves the way it does allowed him to create a vibrant sunset without the help or mother nature (or any highly advanced compositing techniques in post).
"Why" Provides the Freedom To Pre-visualize A Result
Photography involves a great deal of experimentation, nothing will ever change that. You, however, are able to reinforce your efficiency by learning why each of your given techniques function as they do in expected situations. Then, by leveraging that knowledge you are able to predict what those technique will do in unexpected situations. This knowledge allows you to solve problems before they are encountered both allowing you to arrive at the shoot better prepared but also allowing you to be adapt rapidly by transforming potential catastrophe into opportunity.
A good example was when I was shooting the image of this Scarlet Witch cosplayer below. While setting up for this shot I knew that I wanted the entire scene to be bright red. I also knew that I didn't want my model to be bathed in bright red light. The super cramped location meant that I wouldn't be able to use normal technique to achieve the lighting that I wanted. Instead, I had to become creative by leveraging my understanding of how light behaves to create the image that I had visualized in my head. Perhaps a few of you can guess how it was achieved in the comments below? Photoshop was only used to add the special effects and to pump the saturation. The light and color was all achieved in camera, in a single frame. The space was incredibly cramped and pitch black so we had to come up with a solution that didn't depend on any large modifiers. There are three speed lights used in this shot. The only modifiers used are gels. There was no available light.
As photographers, we should also be learning new things; it's critical however, to deepen your knowledge as well as expanding it. When learning new technique or how to use new gear always stop and ask yourself about "why" it works. Learning what to do is easy but leaves you enfeebled and powerless when the "what" doesn't work for one reason or another. Be the photographer who is able to face problems that don't have obvious answers as it will vastly increase the value of the work you do.