When you work with multiple cores they'll likely share the same L2 or at least L3 cache. Multiple CPUs often you pay the cost of copying that L3 cache over or need an L4 or worst case you go back to system RAM.
Each level that you go out further can drastically reduce performance, so you need to try and stay on nearby cores where possible.
Most devs don't account for that since dual CPU machines are in the vast minority
When you work with multiple cores they'll likely share the same L2 or at least L3 cache. Multiple CPUs often you pay the cost of copying that L3 cache over or need an L4 or worst case you go back to system RAM.
Each level that you go out further can drastically reduce performance, so you need to try and stay on nearby cores where possible.
Most devs don't account for that since dual CPU machines are in the vast minority