This kind of micro-optimization is bad practice. In the vast majority of cases, the Windows task scheduler and the developers behind the application in question make pretty optimal use of available cores on a system. Unless you're working with software that has very specific requirements it's best to avoid this kind of tweaking.
Unless you optimize every process like this, you're actually making the system less performant.
Also, you can tell Windows which to favor. Go to system properties > Advanced > Under "Performance" click Settings > Advanced and you can choose to favor either programs or background services. Though, to Windows, a service are those processes spun up via things found by running services.msc from run.