My normal approach is to measure and set up separate alerts for "error rate" and possibly "timeout rate". You definitely want to know about those, but "mean lat

My normal approach is to measure and set up separate alerts for "error rate" and possibly "timeout rate". You definitely want to know about those, but "mean latency" mixes those metrics with the latency metrics for successful requests, which makes it less sensitive to changes in either one. In general I agree that averages aren't always bad. One additional advantage is that it's often possible to generate robust confidence intervals for averages, but it's often not valid to generate CIs for medians/percentiles without introducing other probably flawed assumptions.