iOS 9 includes a new feature that allows you to download just the parts of an app needed for your device. This saves storage space on your iPhone, iPad, or iPod touch when you install an app that supports this feature. After you update to iOS 9, iTunes isn't used to restore your apps when you restore your device. Instead, optimized versions of your apps download from the App Store directly to your device.
If you can see the apps on your iPhone, iPad, or iPod touch, and they appear to be waiting to download, make sure you're connected to Wi-Fi or the Internet. After you're connected, optimized versions of your apps automatically download to your device.
Similarly, apps that you add to your iPhone, iPad, or iPod touch don't sync or transfer to iTunes on your computer. If you want to download apps to iTunes, turn on Automatic Downloads in iTunes Preferences. You can also download previously purchased apps from iTunes.