If you're worried that your Windows Mobile device storage might be too limited when Windows 10 Mobile finally releases in a (*ahem*) few weeks, Microsoft has an app that should help ease your mind.
On July 22, Microsoft delivered an app in the Windows Mobile app store called UpdateAdvisor that cleans up temporary space and then can be configured to move specific data to either your SD card or OneDrive – or both. Additionally, the app checks for Windows Mobile updates once the cleaning process is complete.
Using the app if pretty easy, but finding it by searching in the Windows Mobile app store is difficult. To get to it right away, you'll want to plug the following link into your Windows Mobile device: (https://www.microsoft.com/en-us/store/apps/updateadvisor/9nblggh0f5g4).
Per the app listing, you can…
Move songs, podcasts, pictures and videos to your SD card.
Move songs, podcasts, pictures and videos to OneDrive.
Delete songs, podcasts, pictures and videos from your phone.
However, I've yet to find the option to actually delete items. I'm sure the app will be improved the closer we get to the official Windows 10 Mobile release, but its still a useful utility for just maximizing storage for your device.