Implenting essential functionality like indexes, foreign keys, triggers and other niceties would be perhaps fun to work, but it would be quite the effort to replace the value-added that comes with a professional RDMS.

if the data involved is small, and would equate to a couple of isolated (no relationships) tables, then perhaps a flatfile scenario would be ok. but if you want to restrict columns to domains of data that would reside elsewhere (another table, file) then not leveraging what others have spent decades building would seem to be a bit illogical.

Even lightweight databases with minimal advanced capabilities (i.e no stored procedures, triggers, replication, recovery) in most cases would still be advantages (IMHO) to using flat files. Today it's only one or two tables/files, but when does any meaningful project ever stay static?

but I agree with your friends....it would very well "depend"

I think this is a great topic. thanks for posting it...