ADB is the main command line tool for interacting with Android devices. It can be used to sideload APKs, copy data, and more. Starting with Android 4.0 ICS, a feature to backup and restore applications (and their data) was added, but that functionality will be removed in a future Android release.
A new commit to the Android Open Source Project (AOSP) adds a deprecation warning when using ADB's backup and restore features. In non-technical terms, it means the feature still works, but it will be removed at a later date.
It's not immediately clear why the functionality is being removed, but there could be a few different reasons. The growing use of app bundles means that restoring backups to devices other than the original source is becoming more impractical. Android also has more built-in options for backing up app data than it did in the Ice Cream Sandwich era.
- XDA Developers