I am a freelancer in this area. Microsoft Analytics Platform System is a suite of many different products. I have been busy using Microsoft Analytics Platform for the last 10 years and it is not really one single product. There are many different tools and many different technologies used both on cloud and on-premise. It is maybe a hundred products. There is not one single component that I would call Microsoft Analytics Platform System because it is just that: a system.
Because that is the case, it is very difficult to pick one thing as most important or that we use it for most because it is so versatile and serves very different needs for different users. Sometimes a part of the suite is used by just a couple of people and sometimes by a complete team or even groups of teams. It really depends on the situation and the solution the product provides for a given project. No part is the primary part. I could only say that the use case is to work with a unified system to enhance collaboration, analysis, and productivity, and only that.
Personally, I get assignments from companies and I then implement those assignments for those companies. I, myself, do not use those products at all. So I am not going to use more or less of a particular part or service. I go to the assignment and I implement the solution in Microsoft Analytics Platform System for them. I do all kinds of different projects, from small to medium to very big. My personal use case is to do the implementations for projects for those companies.