Apple made a major change in the latest version of iTunes, version 12.7: they removed the App Store. And because of this, you can no longer sync apps using iTunes.
But many people think that this means that iTunes no longer backs up your iOS devices. It still does, exactly as before. iTunes backs up much of your data via iTunes (you can also back up your device to iCloud), but it doesn’t store apps; it never has. It merely stores a list of apps and how they are organized on your device. When restoring a device from a backup, it used to copy the apps from your iTunes library. Now, it downloads them directly to your device, which, as I point out in this article discussing what’s new in iTunes 12.7 can be problematic for many people.
It’s a good idea to back up your device to iTunes, because it’s a lot faster to restore a device, if you need to, and it’s more reliable than depending on what may be a slow internet connection when you need to restore a device from iCloud. I back my devices up to iTunes regularly, then back them up to iCloud once a month or so, in case I need to restore a device when I’m not home (something that has never happened to me).
Note that iTunes does not back up content that is stored in iCloud, such as your contacts, calendars, or notes. It also doesn’t technically back up your photos; it imports photos that aren’t yet in your Photos library (assuming you don’t use iCloud Photo Library, and the photos have synced already to the cloud).
So, keep backing up your devices as before. iTunes hasn’t changed how it handles these backups.