At noesis.gg we made a small, not-at-all scientific comparison of our JSON and flatbuffers implementations: https://www.noesis.gg/news/player-movement-speedup.html.

The somewhat silly video on that page shows the actual difference in performance our users felt after the change. It was a _huge_ benefit, both in terms of loading time, but also in terms of memory, vastly increasing the number of CS:GO rounds that could be analyzed simultaneously.