I think what the OP means that using Docker you can use tools that give horizontal scaling for free (see: Cloud Run etc.)
Maybe it will be some day, but these orchestration and deployment tools built on Docker have enormous hidden costs.
IME, Docker takes an enormous amount of focus away from the customer problem and moves it to the how to get this mess working problem.
Now may be the right time in a given business to make that shift in focus, but to claim that it will be "free" is just misleading (IME).
This is the opposite in my experience: Docker lets me focus on the business problem by making deployment easier.
At least, that's been my experience when maintaining a mess of other people's Docker crap.