Hint: If you added more calendars to the bar, please note that you can swipe it.
The favorite calendar bar allows to quickly hide other favorite calendars except for that particular one you currently withe to view. To use the bar this way just long-tap the calendar you want to focus on. If the long press was successful, every other calendar will disappear and you can have an undisturbed view over a certain calendar, i.e. the "Private" calendar in the following screenshot.
If you want to add or remove favorite calendars, you have to access the calendar menu of the Business Calendar first.
1. open the Business Calendar 2 and the navigation drawer by swiping from the left edge of the screen, choose → Calendars & Task lists
2. every calendar with a filled star-icon is currently highlighted as favorite, any change will appear in the favorite calendar bar immediately