In short: always use the clean workbook feature before inserting an element in the Excel library!
When used for a long period, workbooks often become overloaded with a large number of corrupted range names (our support team often see workbooks 10 000 to 100 000 names). These names do not refer to anything anymore, but they can significantly increase the size as well as slow the saving, opening or closing of the workbook.
If not removed beforehand, these names will be transferred to the library. Note that UpSlide might warn you about these names while none are visible in Excel Name Manager (they can only be un-hidden via VBA code).
Similarly, workbooks used over a long period of time, and especially workbooks initially created with Excel 2003 can contain a very large number of unused cell styles (visible in home/styles, see below) with dire consequences to the opening time of the workbook. If not removed before inserting items into the library, these styles might considerably slow the insertion of library items.
With UpSlide clean feature, you can effortlessly remove all this waste.