A quadcore computer should max at 4 workers. We don't suggest throttling it to include hyperthreads. With that said, let's say you have 4 additional HT and you start a pool of 8 workers, perhaps you get even a 10% increase (for example), then maybe it's worth it. You just shouldn't expect an 8x improvement.
Setting the JobStorageLocation is only a suggestion if you are running MATLAB jobs on an HPC cluster and in some sort of rapid batch mode. For example, you write a PBS job script to run MATLAB code that uses a local pool. And then you submit a slew of those at once. In that case, setting the JSL can be helpful (due to a race condition).
The number of workers used is the min(M,size-of-pool). In your example, that would be 8 and 4 respectfully.
