I’ve worked on similar experiments (starting about Stories) and we included long-term holdout experiment to measure the compounded impact of sharing. The fear at the time was more about professional content (with millions of views) vs. your friends. The worry was because people engaged more with the former but posted more if they saw the later.

I left before conclusions were drawn, but (according to press reports) those experiments changed the goals to more leading indicator of long-term trend, like posting rather than Likes. I joined again more recently and expected to see that it influenced the company.

I’m not working there at the moment.