In a blog post, YouTube explains:
This new look includes longer video titles and larger, richer thumbnails to give you clearer information about the video at a glance, plus higher resolution video previews. As part of this cleaner design, you'll notice we've also removed some content shelves. You can still find rows of videos for breaking news, music mixes, and more.
Additionally, YouTube added an "Add To Queue" option, making it easier for users to quickly create video playlists. This is roughly similar to Spotify's "Add To Queue" option when adding a queue of music.
Initially available for mobile users, YouTube also made its "Don't Recommend Channel" option available for desktop users and will provide additional control for YouTube content recommendations.
Although these updates are minor, they nevertheless should improve user experience for desktop and tablet users.