Mashable:

Phone Expander is designed to make it easy for a user to easily save space on their iOS device by deleting cache files inside apps, easily remove large apps installed on the device, remove pictures or videos (backing them up to the desktop first) and soon, manage music on their devices.

I ran the app on my (backed up) iPhone and it allowed me to recover a little over 2.5 GB. Not a lot but every little bit counts.