There is no benefit of io being async in itself until you have many users. The immediate and more accessible benefit is speeding up individual requests due to the ease at which you can perfom io in parallel. But if you just sprinkle await/yield everywhere (which everyone unfortunately does), you don't even get this benefit.
I am referring to usage of generators without promises (or rather code that uses generators in a way that it wouldnt matter if promises or thunks were used). And even then I didn't say that you couldn't, even when using promises and generators together most people make their code unneceasarily sequential.
