The daily() function returns a timeseries array of values in a daily cadence. It can only be applied to As Of and Per Day metrics.
Note: while allowed, the assignment of this function to a per day metric would have no effect since the per day metric would inherently be translating the values to the per day cadence.
This function would typically be used to assign an attribute value to a metric timeseries array.
Syntax
daily(value)
Argument  Description 
value
(required) 
A constant (i.e., hardcoded value or attribute reference). 
Where Available
 Metric expression
Examples
Where  Example(s) 
Metric expression

daily(headcount__c)
This would apply the value in the head count attribute to the metric’s daily time periods.
This would return the number of days in the year. 