Excel has a few issues that I've seen when getting the data into SSIS, some are technical some are users. It's great because it's flexible but this is also one of it's issues when processing data
It's not WSISG.
It's not relational.
It supports mixed data in columns and then provides meta data based on a sample of the first few rows.
It can mangle dates, particularly when switching between different regional settings.
Formatting can make a 3 row sheet look like a 16000 row sheet.
Users like to put extra rows with comments or messages at the top.
Worksheets get moved about and relabelled.
Users put important information into comments or have significance with regards position or colour of cells such as creating calendar data in excel.
The one thing that I've seen SSIS excel with (pun intended) is converting a pivot chart back to relational data. I unsed an unpivot followed by a conditional split and a merge join.
