Newrelic is an awesome tool for RUM. Unfortunately it does not allow you to instrument custom frontend events. As an example, Newrelic gives you information about time to first byte, and page load. However, what if you want to track the time async loading of a particular script file took, for example, you would be stuck.
Instead, User Timings is a not so widely used mechanism to track custom events. You can track when your script finally finishes loading, how much time a user spends doing something and other time periods. You can then view distribution by geoghraphy, by browser and even view the time buckets these events fall under. Cool stuff!