The GrandTotal formula returns the grand total for the given aggregate formula. GrandTotal is shorthand for Subtotal(aggregate, "grand_total").
aggregate (required) - The aggregate formula to use in the function.
Count(), Sum([Sales Amount])
In a chart visualizing order counts per Product Type and Region, you can add a calculated column with the formula to the tooltip:
To see an overall total count of distinct orders across all categories.
The calculation is shown in the tooltip in this example, but is usable anywhere an aggregate formula is allowed.