The approach scales throttling in such a way that you shouldn’t notice much if anything unless the situation is truly dire. At that point, Zuul is likely throttling heavily to protect both the service and itself — there’s a total outage if Zuul stops working.
You’ve already witnessed this system in action without realizing it. Netflix encountered a problem in 2020 that was similar to the one behind a 2019 outage, but the load shedding worked well enough that playback kept working even while the system was recovering from a failure. The company is planning to fine-tune its approach further, such as dynamic thresholds for when throttling kicks in.
This doesn’t guarantee that Netflix will avoid all outages or other degradations going forward. After all, the company did reduce bitrates to avoid clogging networks when pandemic lockdowns began. These failures should be less likely, though, and might not last as long if they occur. That’s particularly crucial when there’s an abundance of rivals. If Netflix ran into too many outages, it risked losing subscribers who’d be willing to give up a few exclusive shows if it meant more reliable streams.