So if your website receives no requests, it costs you nothing. And requests have less latency for the user.
That's the theory anyway, in my experience reality is a lot more nuanced because the serverless node still has to reach a database and so on.
PHP in WASM means developers can run actual, real, native PHP code in the user’s browser, without the user needing to have PHP installed locally, or nginx, etc…
“At the edge” basically means “close to the user”, with the details left as an exercise to whoever is selling you their “edge.” In this case, it’s a Wasm runtime company.
But yes, for full blown applications udually talking to a cache and a DB there are way more efficient and performant solutions already.
The problem in practice with Cloud Run (and similar products from other providers) is that it can take seconds or minutes for the platform to detect idleness, during which you're still paying, and then seconds to wake up -- during which users/clients have to wait for a response or possibly leave the service/site.
For my taste, real scale to 0 would be: detection and scale to 0 within < 1 second of a idleness, and wakeup within an RTT, such that the mechanism is transparent to end users.
As a shameless plug, this is what we do at kraft.cloud (based on years or research, LF OSS work, unikernels, a custom controller and overall non-negligible engineering effort).