I’ve moved your question from the Support category to the ROCK category, since it is more of a general question rather than an issue that needs to be handled by the Support Team.
All the database stuff happens on a single thread. DSP can use more than one thread (at least for some stuff), import analysis also does (can be configured in the Roon settings depending on the CPU), and each zone output can also use a separate core.
As you can see, the single core performance is essentially the same. The number of cores becomes bigger, so it depends on what you want to do. See the post above for what benefits from more cores.