and then there is a decent amount of software that's mostly "one and done" and has immense performance constraints - games and anything that has to do with real-time. for game engines, a custom data format from the very start makes a lot of sense because your budget is usually less than 17ms and 8 threads on low-end hardware and 8.(3)ms across 16 threads on high-end. there, "smart data structures and dumb code beat dumb data structures and smart algorithms" couldn't be more true.

yet, for a generic app or server, just don't fuck your brains and go with SQLite