“We’re implementing ad limits because very high ad volume can hinder an advertiser’s performance. With too many ads running at the same time, fewer ads exit the learning phase and more budget is spent before the delivery system can optimize an ad’s performance.”
So, according to Facebook, running too many ads leads to worse overall ad performance. Which could, eventually, reduce overall ad spend because effectiveness is impacted -if more big advertisers start to complain about poor Facebook ad results, that could slow all advertisers in their spend.
At least, that appears to be the theory.
As noted by Facebook, the change will only impact a small number of brands, so it’s not likely that your business will be affected. Marketers will be able to monitor their Page’s ad volume via the new Ad Volume API, with the change going into effect mid-2020. Expect further details before then.