Exporting simple tabular SSRS reports to Excel usually doesn’t create too many problems. But what about those reports with multiple regions (maybe mixed matrix, table or reports) and textboxes external to regions? These can be a different case altogether and are particularly prone to producing reports with merged cells.
Of course, merged cells are not necessarily a problem if all you want to do is view or print your Excel workbook. However, they can make it impossible for you to use filters or work with the report data in any meaningful way.