The Date type fields within ‘Display By’, ‘Group by’ and ‘Stacked by’ selections support different formatting options. One of the options is ‘Exclude empty …’ that allows to filters out all empty records appearing on the x-axis from the given date range.
It is used in majority of cases to calculate average values by excluding the non-working days (i.e. the dates without value).
Here is the difference on the chart:
Please check following recording with its usage: