It's a fair question, but mostly irrelevant in this context. As long as users feel engaged with the site and are using it (and thus watching ads), it doesn't matter how long a users's 'watch later' list grows.

I say "mostly" because there's likely some small effect from users who get overwhelmed by the length of their watch list and bounce from the site, but it's hard to avoid links to YouTube if you spend any time on the Internet.

The YouTube links thing is an interesting point. I wonder if that’s how Facebook’s decision to be a walled garden will come back to them. They prevented other sites from indexing and linking to content, but as a result there’s not as much organic traffic into Facebook to reactivate lapsed users. They planned for growth which will hurt their decline.

The walled garden will continue being lucrative though. Especially if they win VR.

Yea a portion of the watch later. The main signal there is that the recommendation engine is so much better than I see tons of recommended stuff that I automatically add to the watch later. In the past it was always - watch one video and bounce because there was a lot of low quality, irrelevant videos recommended.