asynchronous - Parallelization by threads vs Parallelization by processes on backend - Stack Overflow

I used to work with usual sync programming and the archtecture implied that if you need anything to run a parallel, you queue it in message system and you would spawn extra process on the same or other VM to consume it : quite mild resource usage spikes, especially when you limit the number of certain processes on VM.

I have seen asynchronious programming when you parallelize (potentially but) your actions/work within the process which in its way leads to less controllable bursts of usage of resources (CPU, memory).

Am I wrong? Is there any criteria/guideline to prefer 2nd over 1st?

The question is about async programming on backend side.