Hey Brad,
This would be an interesting tie in with your Time Tracking reporting to answer questions like "where are my resources spending their time", "how far above/below are a given resource", or "what team has bandwidth for additional projects". I do not know that there is any OOTB content that directly answers this, but I could see how this could very easily be managed within an Apptio platform solution.
Edit: This is assuming this is Labor Resource capacity. Though same could be said for non-labor resources, just different data.
-Greg