From a customer:
We are looking to get performance measurements for various actions throughout the app in a given session. With your Custom Timings API, we can easily track the launch time of different pages and resources, but we are also looking to get measurements on how long it takes the app to respond to a user action. For example, during fast forward, we would like to measure the time it takes the app to change from a seeking state to playing state. Since a user can perform this action multiple times in a session of the app, we would need to record this time and send the data several times in a session.