If you were scrolling through the home screen on your iPhone and one of your most critical apps suddenly turned dark and renamed itself "cleaning...," you'd probably panic, right?
"What's going on?" you'd likely ask, imagining tiny scrubbers wiping your app clean of all the information you've gathered and stored on it during the last couple of months. As ominous as this message might seem the first time you see it, as soon as you open the app you'll realize all of your data is still right where you left it there was no need to worry after all.
So, if Apple's hidden cleaning bots didn't scrub away your data, what were they doing inside your app, and who called them?
The "cleaning" message simply means that the operating system on your iOS device (yes, this also happens on iPads and even iPod Touches), is clearing out excess temporary files associated with an app. This process typically kicks on when the device is nearly out of available storage space. In an effort to clear out a bit of extra room and keep itself from dragging, iOS turns its attention to apps that may be bloated with local cache data. Cache data is simply information, typically media or webpages, that apps like Facebook, Instagram and Vine download and temporarily store for quick viewing.
By clearing these downloads, iOS typically opens up a few hundred MB of space. While this isn't a whole lot, it does clear a runway so that the device doesn't have to display dreaded messages like this: "there is not enough storage to take a photo." If you notice your device kicking into cleaning mode, it's probably time to back it up and clear some space. The easiest ways to do this are to move some saved files, like photos, videos and music, off of your phone and onto your computer or an external hard drive.