The one I’ve seen was a client who wanted to store credit card numbers in an Excel sheet (yes I know this is a bad idea, but it was 15 years ago and they were a scummy debt collection call center). Signed integers have a size limit, which a 16 digit credit card number significantly exceeds.

Now, you and I know this problem is solved by prepending ‘ to the number and it will be treated as a string, but your average Excel user has no understanding of types or why they might matter. Many engineers will also look past this when generating Excel reports.