"Build a man a fire and he'll be warm for a day.
Set a man on fire and he'll be warm for the rest of his life."*
I'd never heard of parking and unparking cores, thankfully Google has. As far as I can tell there is unlikely to be any performance gain as if the game that is running is demanding the cores shouldn't be parked anyway. It appears inactive cores are shut down, or parked, until they're needed, if the game requires a lot of CPU resources I doubt any would be shut down.
Perhaps the time saved manouvering them out of the parking space without dinging that shiny new i7 parked in front is making a difference for the OP though : )
Whatever, I thank you for posting this, it's always nice to learn something new.
*Thank you Sir Terry.