my father in law has a vw caddy (sdi). it has something like 120k in it even though it looks beaten up. i once told him I'm surprised. he told me that's 1.120.000km as the analog dial goes back to 0 after a million
Without persistent data structures (structural sharing) - every change requires copying the entire data structure, memory usage explodes, time complexity suffers, GC pressure increases dramatically.
With persistent data structures - only the changed parts are new; unchanged parts are shared between versions; adding to a list might only create a few new nodes while reusing most of the structure; it's memory efficient, time efficient, multiple versions can coexist cheaply. And you get countless benefits - fearless concurrency, easier reasoning, elimination of whole class of bugs.
I would also block/reject a person like this. I had my fair share of these phishing attemts so I'm not asking questions if someone is trying to touch my infra.