No it's not because you never know what other data is quietly hidden somewhere else in that monstrous opaque file. MS Word used to silently include deleted text

No it's not because you never know what other data is quietly hidden somewhere else in that monstrous opaque file. MS Word used to silently include deleted text to help it save/open files faster! You really need to look at all the bytes in the file to be sure, which means export to CSV, or I suppose unzip the XLSX file and hope there's no binary data. The same goes for metadata in images, and any other complicated opaque file format. It's automatically potentially full of things you don't know about unless you're an expert on that particular format and software, which no government Excel user is.