While this is concerning, smart advertisers were looking at the distribution of view length percentages anyway as you can easily pull those columns in and their derived metrics.<p>Likewise, smart advertisers look at lift in conversion metrics when possible, in which case this stat is irrelevant.<p>That said, FB has not exactly helped things by making metric definitions a little obfuscated in general.<p>Personally, I see a bigger concern is them giving 100% view through conversion credit with a 1 day window by default as part of any website conversion action tracking. There are very few cases (like some retargeting situations) where you'd ever want to give full weighting for a VT, and while there is likely value in VT's, I probably wouldn't give 100% credit to them by default given the rate at which people scroll on mobile. But advertisers like to see big numbers, agencies like to show big numbers, and so you have platforms like FB aggressively try to push metrics like this and some of their rather loose definitions of "engagement" without great explanation of the nuances or pros and cons. These are largely left up to the advertiser to determine since, to be fair, they are very subjective.<p>Savvy buyers know this and configure their reporting and tracking settings accordingly because FB and PMDs give you those options. They are sometimes just buried.<p>Ultimately, IMHO FB and Google's greatest defense towards any of these sorts of claims is better and (more importantly) transparent attribution data and tools. If they can prove their value on the bottom line, other things often don't matter to many advertisers. Attribution is a tough nut to crack, but for advertisers spending large sums, it is critical to be successful in these channels.