Comment by belthesar

A super smart guy on my team at a previous job replaced around $100,000 of server and SAN hardware used for a(n) (admittedly incredibly absurdly designed, well before our time) analytics system built using MySQL filtered replication triggering stored procedures in this magical Rube Goldberg-ian dystopia with a 3 node Flask app running with 2 cores and 4 GB of RAM each performing the analytics work JIT. The app would use in-memory SQLite3 tables to perform the same work as the stored procedure operations, and cost about 50ms of extra time per request for a feature of the app that was rarely used.

Admittedly, not high traffic like you asked, but one of my favorite uses of SQLite hands down.