"Don't care where it runs, don't want to manage it, I want to pay only for when I actually use it, thanks for managing it, here's some extra cash for the effort"
But you can only apply that metric if you remove the end users from actually touching the machines (virtual or real).
This is the "less" in serverless.
Turns out that this is also something people want: not having to be on the hook for actually administering machines, installing security patches etc etc.
So managed (platform as a) service + fine grained billing
