YouTube is reportedly testing a new Smart Downloads feature that downloads 20 videos each week based on your viewing preferences. Of course, the app will only download the content using Wi-Fi. The mission is to store mobile data when you are on the run and watching your favorite channels.
The new feature can only be accessed by Premium subscribers in Europe. You can activate it through Settings> Try new features> Try it. You must do so before February 14 to participate in the test phase.
The app will always notify you if you run out of storage space before downloading any videos, and you can view the downloaded videos on the Library tab with the rest of your downloaded videos.