I use CSV (really tsv) because big data tools can open them extremely easily, because they're human readable, and because they're easy for my software stack to parse and use. I do most of my data processing for local consumption on a repl-like tool. We have a defined configuration for TSV we use internally that is lossless in terms of storing and extracting a number of complex data types. Embedded JSON with embedded separators in that JSON? No problem.
Originally the xls format was the only open format in the office family and it was actually much easier to create xls files than to deal with the stupidity of csv
I take a defined format like .xls over an unspecified de facto ‘standard’ like .csv anytime. In many locales .csv files don’t even contain comma separated values because the comma is the decimal symbol already. It’s a mess, half of the time Microsoft can’t make it work either even when you only use their software.
