I've seen a few posts on this so wanted to summarize the fastest yet bulky way to get videos off.

1.  Moving files out of the app process.  So far the "best method" I've found is:
1.  Connect phone to iTunes
2. Go to apps, and copy the hg300 storage folder to your computer.
3. Delete the app and redownload the app (clearing cache definitely doesn't work for me - app will show "0M" stored but when I check iOS settings, it'll show lots of storage taken up).  Make sure that you're on wifi when downloading as the app is larger than 100MB.

General bugs/design issues found:

1.  Photos don't show up consistently.  Sometimes I see them, sometimes they're not in the UI of the app.

2.  Clearing cache doesn't work.  This shouldn't be an issue really. The real feature should be when I delete them from the app, they should get deleted out of the cache.  I haven't seen a way to recover these files so why are they kept around after user deletes?  I'm lucky in that I have a 256gb device but DJi Go still took up 128GB in about a week of heavy filming and deleting!

3.  Let users select to save files automatically to device (or at least in bulk).  Video export method is way too slow - I can have 50-100 videos a day and would have to spend time to get them out of the app - luckily the iTunes method outlined above seems to work well but the best workflow would be to simply to allow users to choose to save the file to iOS photos automatically or as default without saving in the app.

Hope can get these issues worked out.  Really love the Osmo mobile and the hand control setup - now if the app was as intuitive it'd be great!

For me I found a better way:
iXpand Drive from SanDisk. I've bought the 128 GB Modell.

Easy and quickly you can copy your files from the iPhone to the 126 GB Stick (iXpand). And then put the iXpand in the USB-Slot (USB 3.0) in the PC and copy to a Harddisc. It is also possible to copy Videos from the pc to the iXpand and then to the iPhone.
When traveling, it is good when you have filmed a lot, you can then in the evening the movies on the notebook copy and delete on the iphone again. I don't Need iTunes.

Hi, please update your DJI GO to the latest, and you can delete your photos/videos in "Library". I checked my iPhone and I see the available storage in system increased, which means the spaceis actually released.

DJI-Thor Posted at 2016-12-9 11:22
Hi, please update your DJI GO to the latest, and you can delete your photos/videos in "Library". I checked my iPhone and I see the available storage in system increased, which means the spaceis actually released.

What LIBRARY are you talking about??

Jack

DJI-Thor Posted at 2016-12-8 19:22
Hi, please update your DJI GO to the latest, and you can delete your photos/videos in "Library". I checked my iPhone and I see the available storage in system increased, which means the spaceis actually released.

I've done this in the latest version of the app and it just looses reference to those files (not actually deleting them).

For example:
1.  I have 10GB of videos
2.  Attach to iTunes and copy off hg300 storage folder
3.  In the app on iOS, delete the files via manage in the library
4.  Check the cache, it says zero
5.  Quit app, open settings > general > storage
6.  DJI Go still shows 10GB
7.  Go back to DJI Go
8.  Shows 0M cache - Now the files are not accessible in the app, but still show up as taking storage to iOS.  
9.  Connect back to iTunes and look at hg300 storage folder - size is same

Other issues:
PHOTOS:  the photos I took within the DJI GO app do not consistently show up.  If I take a photo and look in photos, it'll show up.  But if I quit the app, the photos no longer show up.

TIMELAPSE:  I have similar problem - they don't show up in Videos, I have to pull them off via iTunes

Honestly, what I'd love is that if the controls on the OSMO could switch between the built in iOS camera modes of photo and video and do something like zoom so that I can use the built-in iOS camera app and save directly to my camera roll instead of going through all of this.

I'd only switch to DJI GO app for panoramic or timelapse modes

I think that clear ios app cache is very important measure to free up my iPhone space. Usually I will back up my data via iTunes at first, and them I will move my app files off iPhone by manually deleting them. Lastly, I will wipe the file cache as well. This help me delete data from iPhone completely and permanently. Also, I will apply some third party apps to help me erase my iPhone data sometimes.

This is an powful software that can clean App  cache on iPhone and you can even delete other data from iPhone for cleaning iPhone.
https://www.safewiper.com/ios-data-eraser.html