The ability to manage "Totals" in a Table or Matrix

Currently, whenever displaying data in a table or matrix, a total is presented on the bottom that cannot be adjusted. It would be great if we could be able to manage it. Instead of summing all the values, being able to have the ability to subtract certain rows from others, finding the average of all the values in the column, and other common math functions. This would be really helpful in building financial statements such as a profit and loss. You can have revenues and expenses both in the same table and be able to display the operating profit below instead of summing the two together. This will also reduce the need for a measure.