HI @Molly - hope you're keeping well!
Just to clarify a bit - it's really dependent on the 'size' of the logged-in user program.
Let's just use an example of a site that sees 100 unique visitors a day, 50 of which are frequent users of the site each day.
If all 50 of those users sign up to be logged-in without ads, you could be cutting your revenue in 1/2 right away (which you could make up with the subscription price potentially), but more so could be then affecting the ePMV because it's 50% of all users to the site, and the 'best' or highest earning visitors to boot!
Where this wouldn't have such a large impact is if only 5-10 users are signed up as 'logged-in and ad free'. That's 10% or less of your daily traffic not seeing ads, which isn't necessarily a large enough group to really impact ePMV (again, you'd see a revenue loss initially but in theory could make up with the subscription price).
We don't mean to discourage you from a business decision - we just wanted to make sure it was clear that there could be fall out if not implemented properly, and that you were fully aware of potential revenue loss as a result.
From experience - there's usually not a massive percentage of visitors that opt in to this sort of 'ad free experience', especially initially when it's introduced on a site. If it's something you're really interested in trying, the 'initial' period could be used for testing. As in, you're welcome to try it out and see the impact - we will be here to help as needed regardless 🙂