Establishing and maintaining performance metrics has one primary benefit for teams as they grow. They are good for provoking conversations about why exactly numbers increase, decrease or go flat.
This discovery of why performance patterns exist as they do requires that we work from data rather than assumptions. It takes no effort to get involved with all kinds of interpretations, predictions and explanations that may or may not be accurate and complete. This is why it's helpful to do this in groups rather than as individuals.
If we don't know why a certain pattern has occurred we are more likely to either repeat it or not be able to repeat it again in the case of failure or success patterns. In some cases we have to test a hypothesis before knowing for sure if it is in fact a contributing factor to any specific performance pattern.