Transferring mobile apps from iTunes (iPhone) to an external hard drive
Backing up your purchases is one approach. Since iTunes provides access to your prior purchases (as long as they have not been removed by Apple or the Developer), you can safely delete them from your computer. That won't be enough though.  You'll need to tell iTunes not to automatically download them.  Here are the steps you could take:


In iTunes, go the iTunes Preferences ( or ⌘, ) and select the Store tab.
Under Automatic Downloads, assert that the Apps checkbox is unchecked. (see image below)
Delete the mobile Apps