Glenn Fleishman, writing for Macworld:
When Apple updated iTunes to version 12.7, it overhauled the iOS/iTunes interaction. We ran a guide, “iTunes 12.7: How to cope with the abrupt changes,” which answered most of your questions. But one thing I noted in passing continues to come up: several readers have asked if they can really, really dump the iOS application files that iTunes retained after the upgrade.
You don’t need these. Really. You don’t. iTunes will never rely on them to sync back to your iOS device, and your Mac can’t do anything with them. Delete them. Go ahead.
This tip freed up 36GB of storage on my Mac Mini. And if you’ve been downloading iOS apps through iTunes, you might be able to reclaim a similar amount of storage on your machine. Glenn goes on to explain how to turn on content caching on your Mac, allowing you to more quickly download operating system and app updates on all the devices in your home.