Welcome to the communnity - if I understand your question correctly - the answer is yes assigning 8 virtual cpus to a vm can cause issues depending on a coupld of issues:
- If your host has only 8 logical CPUs - this will cause constraint on the scheduling of the vCPU
- If there is already contention for CPU cycles then adding an 8 vCPU will only make things worse
I would question the need for for 8 vCPUs - in my experience I have found very few VMs need that amount of CPU power -