People often consider to use this information for reliability and performance, but you can do much more with the data. For example, if a method has low latency, you can use short deadline with fast retry to improve reliability. If you see a sudden jump of certain usage, you can consider to use batching and caching to reduce your cost. If you see an unexpected usage of a service, you know someone introduce a new dependency in your system. Google teams often use the same data to understand how large services work and how they are correlated.

Disclosure: I worked on this feature at Google.