The difference can be quite large, details are workload and software dependent. It isn't just the context-switching overhead (which is prohibitively high these

The difference can be quite large, details are workload and software dependent. It isn't just the context-switching overhead (which is prohibitively high these days), it also significantly improves average cache locality, which is the bottleneck for many high-performance codes. Some types of software optimizations require the ability to correctly infer local CPU cache contents, which is difficult when arbitrary processes are semi-randomly stepping all over that cache.