You can always change CPU settings in the Guest properties/settings later if you wish.
But, in general there is no benefit.
Only scenario I know of where there can be a theoretical (not necessarily real) benefit is if a specific app is designed to and requires a specific number of CPU and/or cores.
But, the way modern hardware (and OS) are designed (SMP processing) automatically allocates and assigns tasks according to the CPU’s internal algorithm, distributing across as many CPUs and cores as there are available.(unless you over-ride). Specifying additional cores might in theory allow the app to think there is improved parallellism, but when you get down to what’s happening in hardware it probably won’t make any difference.
Note also that there is no affinity between virtual CPU sockets/cores and what actually exists in hardware, so can’t partition your tasks.