You can change core affinity from the task manager, but you have to do that every time you start the exe. With imagecfg.exe you change the exe so it will always use the core(s) you want it to use.
While new games use both cores, older games have problems with CPU that have 2 or more cores and can have problems (like crashing) while running on 2 or more cores.
Beware of he who would deny you access to information, for in his heart he dreams himself your master.
Commisssioner Pravin Lal
"U.N. Declaration of Rights"