When metrics are used in key results, then those metrics become important for us in a selected period. That is when we can call those metrics Key Perfomance Indicators. Metrics are the most important part of any Key Result.

When you are providing values for your Key Results at the Check-in event, and if you are using a Key Result based on metric, then you are actually providing data points for the metric itself. That enables the possibility to view on the data from a different perspective, not only from the OKR one.