Bingo. As long as your histogram has the final long tail bucket (>99%) included, you'll be fine. After all, the 100'th percentile latencies are what your user

Bingo. As long as your histogram has the final long tail bucket (>99%) included, you'll be fine. After all, the 100'th percentile latencies are what your users will experience as the worst case. That's what they will perceive and remember. That matters for usability. While there is no sane way to ever eliminate the most obscene outliers, you can target the worst-case behaviour and find ways to limit how badly it impacts your users. Anecdote from work: our exchange team (who routinely consider 4ms for service response too slow) monitor p99 for general performance and p100 for the nastiest outliers. They want to know exactly how bad the performance is for the observed worst-case scenarios.