The 30 second answer
Latency is skewed. A few very slow requests barely move the average, but real users hit them, and one page often makes many calls, so most users see the tail at some point. Percentiles like p95 and p99 show what the slowest users actually experience. An average can look healthy while a meaningful share of requests are painfully slow.
Latency is skewed. A few very slow requests barely move the average, but real users hit them, and one page often makes many calls, so most users see the tail. So I look at p95 and p99.