Initially, U7 only had six classes. When we started working on Minotaur, it quickly became clear that they are all very combat-oriented. Unless someone makes their living by going Outside and, well killing stuff, they needed something else to do. A job to do.
Since we wanted to keep our world consistent, rather than randomly assigning stuff we decided to add jobs to rulebook in addition to classes. Neither is mandatory, just like in real life you don’t have to have a job (or a life, for that matter) or to be able to fight.
Each class has their class skill (manipulation for Aspects, proficiency bonuses for Officers, and so on), and jobs give you unique abilities as well. For example, in Minotaur, Nod can use Axis vision (his outfitter job skill) to help him visualize Axis currents. Which, in turn, lets him solve puzzles.
Axis vision [job] / Active / Self
Visualize Axis currents in the environment.
You’ll be able to try different jobs in Minotaur, where every character except underage Thea has one.