If you want your new data to appear on ROWS, COLUMNS, or in FILTERS in a PivotTable, or on an AXIS, LEGEND, or, TILE BY in a Power View visualization, you must use a calculated column. Just like regular columns of data, calculated columns can be used as a field in any area, and if they are numeric they can be aggregated in VALUES too.
If you want your new data to be a fixed value for the row. For example, you have a date table with a column of dates, and you want another column that contains just the number of the month. You can create a calculated column that calculates just the month number from the dates in the Date column. For example, =MONTH(‘Date’[Date]).
If you want to add a text value for each row to a table, use a calculated column. Fields with text values can never be aggregated in VALUES. For example, =FORMAT('Date'[Date],"mmmm") gives us the month name for each date in the Date column in the Date table.
