Thank you for the link! They were all interesting, and yes, all the result of having a high scale. For anyone curious and thinking about watching the video (I recommend watching it), the topics were 1) should you immediately re-run a failed ad payment (getting paid vs transaction costs/flagged for repeated billing), 2) should you send an IM immediately after a login failure (cost of text message vs possibility user will give up and not reset password), 3) should you fetch data for pre-loading in a web page (higher engagement with page vs cost of unnecessary loading), 4) video upload quality, 5) taking screen real estate for less commonly used UI features.
Interesting examples, and yes, they're all the kind of thing that might not justify the effort for an ML model (and might not have enough data to train) for a small website or operation, but can easily justify the cost and effort when you have a huge number of transactions.
On another note, this is why I often like lightening talks. So many people think that what they're doing falls below the threshold for what is an interesting presentation, when in fact it's the most relevant thing a lot of people will see at a conference.