I noticed the other day after clearing some apps from my ipad that it continued to grow past ~1GB-ish~ until over 7GB. Not really interested in testing it out on my iphone 5S since it'll probably use up all 20GB free...

I'm pretty sure it has something to do with with downloading and creating a local database of the remote media library, as it takes forever to populate and seems to correlate in growth with the amount of size used.