Why would production code coverage data be useful? Because you can use it to find (and then purge) latent code paths in your app. How'd it go at Living Social? Dan says:
After running in production for 30 minutes, we were able very easily delete 2000 LOC after looking through the data. We expect to be able to clean up much more after it has collected more data.
Read more about Coverband on the Living Social Tech Blog.