The Tax Code, traffic lights, your mother-in-law. They all operate in order to compel you or force you to take specific actions. They are systems (don’t be fooled), and they were put in place in order to affect you.
Whenever you put a system in place in order to form behavior instead of simply accommodating behavior that exists, you have a prescriptive application.
Education. If you need someone to do something just a certain way, and then for them to always behave that way, there must be a structure around that need. Either another single person enforces the structure/effect, or a procedure does. A procedure on paper uses the same premise as a video, a diagram, or a person: step through the necessary parts or steps; monitor the output, and reshape it as necessary.
Creating an application that prescribes behavior is a much more efficient way to accomplish the goal. Text, diagrams, voice, video, and more logic can be used simultaneously to effect the goal. It is simply more efficient.
We need prescriptive applications in whatever form because there aren’t enough experts to go around to help us through our problems and solutions in a cost-effective way. When we can use technology to contain much of the same benefit as a person, why wouldn’t we choose to do that?
Transferring the knowledge of a person into a static or even interactive form is no simple task. It involves intense reflection of an iterative nature. It requires the author to put themselves in the shoes of the user; and then to have third parties do the same.
When you codify intended processes into applications, you’re able to shape the way people communicate with each other. You can guide their information into the needed and desired forms so as to produce the desired output. So, whether it is TurboTax, busy intersections, or your hawkish mother-in-law, the job gets done to the satisfaction of the application planner, and your (that is, the user's) behavior is changed in the process.