This trick might come in handy for the folks who use video ads. There are CTR (click-through rate) metrics but there is no watch-through measure. So with one of our customers we came up with the idea:
This rule would increase the budget of an ad set that gets half-video watches for 15% of the impressions it gets. Basically the 0.15 ratio here is a threshold for the watch-through rate.
Additionally you can set up a rule on an ad level to stop ads that have too low watch-through rate. The rule would be pretty much the same, just change the task and the sign in the comparison condition to < (less than).
Sign up for a free 14-days trial to give it a test and as usual, let me know if I can help with anything ;)