Who's who on a movie crew

Why are there so many different jobs on a movie crew? What is one job that you learned about in this video that you'd never heard of. Why might it seem interesting?

There are various types of jobs on a movie crew because people who are specialized in specific districts are necessary in order to perfect a production. I learned about the gaffer for the first time through this video. They're role in the production is to design the lighting for the setting and execute the plan on set. It might seem interesting to become a gaffer on set because different light designs make all the difference for a scene. Being able to create different moods from different lighting designs seems like an interesting job to have on set.