Excel is a powerful tool for tabular, especially numeric, data. It allows you to analyze that data using charts and graphs, and perform calculations based on that data. In previous versions of Excel, the sources of that data were limited. Importing data into Excel either required programming, or it involved a lot of manual shuffling of data once it was imported.
Excel 2003 allows you to specify a particular area of a worksheet into which you can import XML data. Once you set up the map between the schema and the worksheet, you can import new data at any time without having to do any reformatting or shuffling around of data. Excel simply knows where each item of imported data should appear in the worksheet. Because most data is now available as XML, either in its native form or through a tool export, this opens up a much broader set of source data for Excel analysis. You can:
use all of Excel's data analysis features (charts, graphs, calculations) on almost any data
save the worksheets that contain this analyzed data to use as reports
calculate new data from this analysis and save it as XML for use by other applications
