The built-in iOS Calendars app can keep track of all your events and appointments, all in one place. But it doesn't have to keep them all in the same actual calendar. If you prefer to keep your work life and personal life separate, or to have a specific calendar for kids activities, or a special vacation, or for anything else, it's easy to setup. Since each calendar gets its own color, and you have the ability to hide or show individual calendars, it's a great way to stay organized and stay sane at the same time.
Additional calendars are easy to setup, and if you ever stop needing them, they're easy to delete as well.