To measure performance, we tend to rely on central values like averages and median to give us a rough idea of how the performance would be in a normal scenario. 

Averages can give a fair picture when the data is huge and does not include heavy outliers. However, in real life, data contains heavy outliers and thus averages can be skewed, giving us a misleading picture. An additional option of median and 90th percentile values in dashboard, and display median values in our reports tends to solve that.
Median, or 50th percentile, is the middlemost value which means that half the times your performance was faster than this value and half the times worse. Medians are not skewed by the values of outliers.
90th percentile tells you that 90% of times your performance was better than this number but 10% of times it was slower. So this number sets a realistic expectation with customers.