This article is over committing the number of web workers and cores. You should not do n cores = n web workers, it should be at best n-2 web workers (or 1). The reason being this is a consumer device and the cores are absolutely not dedicated to just your app.
That and unless you are purely number-crunching, or the work done by the workers is bursty rather than relatively constant, you browser will want some CPU resource the main thread (and display updates) to be responsive.
It's for non-server machines which will be running other things like the user's browser. You won't get the same performance on the shared cores so sometimes it's better to just run on the free ones, and without checking/adjusting it's just easier to use n-2 cores.
In a production environment you do want to eliminate the other processes.
You want to use better localized memory structures in faster cache, and you want to allow the use of the higher frequency/IPC cores instead of being thermally/memory bandwidth limited by all the cores being loaded at lower frequency all the time.
