To be clear: there's an economic tradeoff to make here that isn't identical at all scales. At a certain point, lost revenue due to user dropoff from availability is more expensive than users who stop using a site due to a frustrating experience (and sometimes that scale itself is the compelling feature able to stave off a user from giving up on your app completely). But in most cases, I think its advisable to start with stronger consistency semantics and only weaken them when a need presents itself. Hell, Spanner is the foundation for Google's ad business, if that's not living proof that you can preserve strong consistency semantics and keep your system sufficiently available, I'm not sure what is.