The Subtotal capability of the Advanced Filter is a very powerful and useful tool for aggregating data.  For example, if you had a years worth of sales data for all your customers and you wanted to quickly find the total revenue, by customer - the Subtotal feature of the Advanced Filter would do the trick.

If you look at the Before and After screen shots below, you can get a quick idea of what I just described.

1. Make sure the data you want to subtotal is in the following format: each column has a label in the first row and contains similar facts, and there are no blank rows or columns within the range.
2. Click a cell in the column to subtotal. In the example below, you'd click a cell in the Company column.
3. Click Sort Ascending  or Sort Descending.
4. On the Data menu, click Subtotals.
5. In the At each change in box, click the column to subtotal. In the example above, you'd click the Company column.
6. In the Use function box, click the summary function (summary function: A type of calculation that combines source data in a PivotTable report or a consolidation table, or when you are inserting automatic subtotals in a list or database. Examples of summary functions include Sum, Count, and Average.) you want to use to calculate the subtotals.   Our example uses Sum for the Qty and Ext Cost columns.
7. In the Add subtotal to box, select the check box for each column that contains values you want to subtotal. In the example below, you'd select the Qty and Ext Cost columns.
8. If you want an automatic page break after each subtotal,
9. If you want the subtotals to appear above the subtotaled rows instead of below, clear the Summary below data check box.
10. Click OK.

We now have the Total (Sum), by Company, of the Qty and Ext Cost columns.

Note: You can use the Subtotals command again to add more subtotals with different summary functions. To avoid overwriting the existing subtotals, clear the Replace current subtotals check box.