If you run a service which allows one to import data, say maybe by uploading a CSV file, than do yourself a favor and store the original file in a place where you can access it later for support or debugging.
Our service allows a person to upload a CSV file containing postal addresses and it has about 8 columns that need to be in a certain order.
Before our code starts to actually process the file we shove it up to S3 in its original form. Later during processing if an error is encountered than a support person can look at the original file and see any obvious errors. Maybe you expect a CSV file but get an Excel (or a Apple Numbers file)? Maybe the customer wasnt paying attention and totally re-arranged the columns. Sure, most of these “soft” errors (such as CSV vs Excel) can be caught pretty easy by inspecting the file extension, but as a whole you are guaranteed to run into trickier situations.
Either way, having the original file on hand for debugging is super helpful. Much better than emailing the customer and asking them to re-send you the file. In most cases we can be pro-active and email the customer back and say “Hi, I saw that you just attempted a data import and it failed, it looks like it was due to ….”