I recently posted details on how to recover gigabytes of lost storage back from iTunes by deleting local copies of apps you can download from the App Store if you need to. Lots of you let me know how many dozens of GB you got back, which is great to hear. Now I have some another tip for you if you're looking for more ways to compress your iTunes library.
iTunes has a habit of spawning copies of firmware files for your iOS devices, which is helpful in the moment if you have to do a restore of your device. But once you've updated to the latest revision, having backups of previous firm updates is unnecessary, since the file is useless — Apple's firmware updates are "signed" with the servers to make sure that you can't downgrade your device.
The net result is that you may have gigabytes of wasted space on your hard drive for firmware files you'll never be able to use again. What's more, iTunes doesn't give you a way to manage these files - you have to go plumbing the old fashioned way, from the Finder. To check for these files, and to delete them:
It's safe to do this - if you need to restore your iOS device again, iTunes will go out to Apple's servers and download the latest firmware update necessary for your device.
Deleting apps from your iTunes library is fine, and you can get back sizable amounts of hard disk space that way - but what happens when you reconnect your iOS device to your Mac to back up?
You'll get a message that looks like this:
In short, iTunes is telling you that it's found software on your iPad that it can't reconcile with the contents of your iTunes library.
At this point, unless you have apps that have been pulled from the iTunes Store, it's safe to just click on the Don't Back Up Apps button. That way your Mac won't waste space backing up stuff you can just download again from the App Store if you need to.
Did this help you save any more space from iTunes? Let me know in the comments.