You shouldn't disable this.
It's nice to have a backup copy of apps, for these two situations:
1) An app is updated, and the update has a horrible bug or took out a feature you really love. If you have the apps backed up on your computer, you can easily roll back to the previous version.
2) An app is removed from the App Store. A good recent example is Blockchain! If you don't have a backup of the app, the next time you restore your phone you will lose it forever. Sometimes developers abandon the iOS platform and stop paying for their developer account. Boom, all their apps are gone.
Apps don't really take much space, and it's a good backup to have. It also speeds up restoring your phone big time, as all the apps will just install from your computer rather than having to download again.