"Count the number of breakfasts" displays the number of guests waking up in the hotel this morning. It reflects either the total number of breakfast covers for hotels offering breakfast to all guests by default or the total potential for breakfasts for hotels that upsell breakfast.
For a report, you can add a new row by following this tutorial.
For a dashboard, you can add the new widget by following this tutorial.
The best illustration of how this widget works would be the following example:
First line - "Count the number of guests in hotel based on stay dates", it shows the number of guests sleeping in the hotel from today until tomorrow morning.
Second line - "Count the number of breakfasts", this widget can also be used without specifying a rate plan, but it just shows the number of guests who are waking up in the hotel TODAY morning.
Since the report in the picture has "daily" format, you can see that the numbers in the first line of the day before correspond to the numbers in the second line for the current day.
The name of the widget comes from the fact that it is mostly used for those hotels that have breakfast included by default for absolutely all the guests.