If you can find a game that will take advantage of more than 2 or 3 cores then it would most likely help but the games today will use 2 cores. There is an option in the bios to park cores? Or arre you talking about diabeling cores? Also diasbling hyperthreading?
Hyperthreading doesn't help gaming in any way and diableing hyperthreading might actually help gaming.
You can see which cores are parked by pulling up your resource monitor and checking. Windows will unpark them as needed, but there is a lot of speculation that you are better to just force them to unparked all the time ( you can do so with reg changes or a utility ).
Everything I've read so far suggests you will see everything from no difference to a huge fps boost to a reduction in game stutter ( if you have it ). I have not yet seen any posts where somebody definitely answered whether there was a downside to perma unparking them.
Which brings me back to the original question of whether there is any downside, added stress, etc from doing so. I'm guessing it is just a power saver, but I dont' know enough to take a chance without asking.
If there is nothing for one of the cores to do then Windows will "Park" it and it's just a power saving feature and something that will extend the life of the cpu. By forcing Windows to "unpark" the core does not mean you can also force Windows to use it. All the cores are there at the disposal of Windows to mke use of them and by Windows parking a core means that there truely is nothing for that core to do.
I have gone into the Windows resource manager as well and observed this parking of cores and I was not disturbed by it and figured that there was nothing that the cores that were parked could do. I have a six core with hyperthreading so there were a lot of parked cores.
It's not possable for there to be a huge increase in fps because games do not take advantage of more than two maybe three cores.
Although I appreciate the above thoughts, I"m not sure any of the answers truly answer the questions of whether there is any known or tangible detriment to unparking the cores.
From my understanding, the parking feature is only in Windows 7. If this is true, then it suggests that cores are naturally 'unparked' in Vista, XP, or other os's from Apple, Google, Linux, etc. And again, if this IS the case, it would imply that there is no downside to it.
That all being said, I dont' know enough to say absolutely if my thinking is correct. So I'm hoping that somebody knows for sure.