Be able to categorize types of exercise so you can then randomize a workout so that you mix things up and don't get stagnant. For example, you could pull together an interval workout based on these categories and the app would just select a bunch of different exercises from these categories in a random but balanced order so you can do a complete, full body workout and just follow the exercises in the order the app prescribes without having to think about what your workout will have to look like on a given day.