As of Loggregator 82 Metrics are now documented inline with specifics about what the metric represents. Here are some searches that you can use to get a summary of all metrics.
metrics-documentation-v1 - These are all metrics related to Dropsonde envelopes.
metrics-documentation-v2 - These are all metrics for the new Loggretor API V2
DEPRECATAED - These are all metrics that will be deprecated in a future release. They are usually adjacent to a new replacement for the metric or no longer provide value.
USELESS - These metrics do not provide a meaningful datapoint and should not be used.