In the old days, you could use 96 (well, 95 to give the client a core) to split serial algorithms across your computing cores. Nowadays, quite a few core operations in ParaView/VTK are multithreaded to take advantage of multiple cores that share memory if you’ve compiled with a symmetric multiprocesing backend (such as TBB) enabled. Hence, you are probably better off most of the time not using MPI at all unless you need to, e.g., you are running on a cluster of machines each with their own memory spaces.