Every Teamup Calendar has a control panel on the left hand side as indicated by the red block:
It hosts the date picker, the list of sub calendars and optionally, the about box.
By collapsing it, more space is available for your calendar. This can be especially useful for printing purposes. To show the Sidebar once more, click the arrow again.
In scenarios where the available screen space for the calendar is very limited, it is recommended to keep the Sidebar collapsed by default. Otherwise, keep it visible.
When embedding a Teamup Calendar in a website, it is often better to hide the Sidebar to allow for more space for the calendar entries to be displayed. You can use a calendar link with a parameter appended to it for this purpose.