Understanding the personality features of someone (or yourself) gives you a tool for understanding how someone might see a situation. Kind of like looking at the world through their glasses.

Tests have been developed over the years (such as Meyers-Briggs) that give a numerical value of being, say, introverted vs outgoing, or intuitive vs analytical. These are often used by psychologists, or as a tool to see areas where partners may be well matched or not.

Signs in Astrology are another similar tool that can be used in this way.

Similarly, the various archetypes found in the Tarot have been used to illustrate various psychological roles, as well as roles in society.