Lots of websites have been relaying a “simple trick to clear space on your iOS device.” The trick, it is claimed, involves renting a movie that’s too large to fit on your iOS device, which then tries to download the movie after clearing out some space. If it is successful, you then have to cancel the rental.
The logic behind this is that the iOS device attempts to clear as much unneeded space as possible in order to receive the movie. While this is successful for some people, it isn’t a panacea, and its effectiveness depends on a lot of factors.
Most iOS users are familiar with that amorphous “Other” storage that displays in iTunes. It’s never been clear what this “Other” storage contains. Apple claims it contains “Settings, Siri voices, system data, and cached files,” but anyone who has had sync issues, and has seen dozens of gigabytes of Other storage on their iOS device knows that this isn’t the whole story.
The best I’ve been able to tell over the years is that Other storage is all of what Apple says above (though I don’t know why they include Siri voices), plus orphaned files, and that these orphaned files are very common. If you use Apple Music, then Other also includes cached files that you’ve streamed (but not downloaded) using that service.
So, about that “trick.” You don’t need to use a rental; if you have already purchased any movies from the iTunes Store, then you can use those as well. Find the biggest movie in your Purchased list – mine is Kenneth Branagh’s Hamlet, at 8.66 GB – and try to download it.
You’re iOS device will hesitate for a bit, delete some files – caches and the like – then it may tell you that you don’t have enough room for the movie. After this, check your device’s storage, and you may see an improvement. I was able to shave off about 1 GB of my Other storage at different times. However, when I repeated the operation, I found that my Other storage increased by a few hundred MB.
So while this trick can save some space, deleting some caches, it’s not foolproof. If you have a lot of Other storage, then try this out; if not, don’t expect it to magically delete that inexplicable yellow band of storage you see in iTunes.