The goal is to predict if, for example, someone is better suited to sweeping the floors vs working with complex systems. Both are useful and respectable jobs but you both want an individual who can actually do it, not someone who just thinks they can, and someone whose capabilities won't be wasted on too simple tasks. These tests are great tools to help you figure out future performances of said individuals, as well as their satisfaction on the job/task. A mismatch will cause impact both for the individual and the company/military unit/etc.