The feature appears to have been first spotted by iOS developer Kaleb Butt who didn't have enough space to download the iOS 9 beta 2 software update.
An alert is presented to the user that reads:
Insufficient Space for Download
In order to make room for the software update, some apps will need to be temporarily deleted. All deleted apps will automatically be replaced after the update is complete. Would you like to continue?
You can choose to cancel the software update or Allow App Deletion.
For more details ahead of the iOS 9 release this fall, please follow iClarified on Twitter, Facebook, Google+, or RSS.