You get what you inspect, not what you expect

Metrics orient people towards what a team values as most important. If you don't measure something, it's hard to know whether you're getting better or worse. As a result, we only get better at things we measure. We do this because it's easy. While you can disagree on how metrics are collected, no one will disagree on which direction they're moving. Knowing this, we need to be careful to measure the right things or we'll optimize the wrong behavior.

Be sure that your metrics work how you expect them to. It's easy to accidentally incentivize behavior that isn't in the team's best interest when the people choosing the metrics are more focused on overall team performance than on how the metrics will change individual decision making. Remember that people will act to optimize the metrics that effect them personally first.