How much cost efficiency is there? I’ve worked at multiple of the top 100 websites in the U.S., and none of them had more than a dozen web servers. For any website, 90% of traffic is logged out and probably doesn’t even hit the web servers.
And web servers are generally the least expensive component of hosting costs.
These costs are more meaningfull for those who bootstrap their businesses and projects at their own expense. I have a personal anectdote where switching from a scripting web framework to a compiled one reduced the runtime size, and the deployable environment went from 800mb to 10mb, which allowed me to fit all my deployments into a free-tier monthly quota of AWS ECR.
Given I already knew both frameworks from fulltime jobs, it's a great net benefit.
It also means that whoever wants to use self-hosted open-source alternatives of user-tracking services (notes, calendars, emails, etc), they can do it cheaper or even for free.
And web servers are generally the least expensive component of hosting costs.