Early on in the project I added support for tagging individual data points. The use case was basically event logging. For example, as a user I query some metric and view its data points in a graph. I then tag one or more data points to indicate some event such as a server restart. This work was done primarily as a proof of concept to see what how we might implement support for tagging. To the best of my knowledge this functionality is not used anywhere. We also support tagging metrics, and that is used a good bit by the Heapster client.
Provided this functionality is not used, I want to remove the relevant code. There is a fair amount of code that if unused as I suspect is just bloat. It also complicates the schema in a way that we could otherwise avoid. I think it makes sense to revisit this code if/when we look to add support for events. Since there are no immediate plans to do so, it makes sense to remove it from the code base.