If you have worked on a large set of data from a non-Excel data source, for example, MS ACCESS, there are chances that you would have stored that in multiple sheets.
This riducules the data management. Now in Excel 2007 and above you have a big Excel workbook with 16384 columns and 10,48,576 rows
Following table gives you how big Excel has grown :)
Excel 2007 and above
Maximum No of Rows
Maximum No of Columns