Videos added to playlists

Found in the engagement section of Studio, and as videosAddedToPlaylists in the Analytics API. It counts saves into any playlist, whether the viewer built it themselves or it belongs to another channel, and Google's documentation confirms default playlists such as Watch Later are counted too. A companion metric records removals, so a strong week of saves can be quietly undone later as people clear their queues. Read it as an intent signal rather than an applause one. A save means somebody planned to come back, which is why it tends to matter more on long tutorials and reference material than on quick entertainment.