[the8472]

If your frontend fires hundreds of requests (which isn't uncommon) then the p99 is merely what most users will experience. Ideally you want cumulative distribution chart that goes up to the max. And then that's just for the requests you measure. If something takes too long the user might do something that cancels the requests which means the backend never completes its response and won't get the time-to-response sample, so you need to account dropped requests too.

https://www.youtube.com/watch?v=lJ8ydIuPFeU

[TiddoLangerak]

This is only true if your latency distribution is fully random, which is rarely the case. More often than not, it's the same small group of users hitting most of the p99 because their accounts are simply more resource intensive.

[the8472]

Depending on how the system distributes work such users can interfere with random with requests from other users through shared resources, so to that cohort these will look like a random latency distribution.