What are the net results/consequences to core parking? As in -- aside from potential power savings, why would one want to have core parking enabled (or disabled)?
Normally in a hyperthreaded CPU the on-core cache is shared between the two threads that the core supports.
The main gain for core parking is that when the system is not heavily multi-tasking the hyperthreaded cores can be parked, this allows the CPU to reallocate the entire cache on each core to 1 thread instead of 2.
What this should mean is that under low active thread counts the computer (such as you would find while playing a game) the actual performance for those threads is higher because they have a larger on-CPU cache.
Multithreaded applications tend to be large data processing applications so the hit from loosing cache is generally compensated by higher availability of processing power when the cores are unparked.
To an extent this is one of those 'best of both worlds' type things, you gain speed when the system is running just a few heavy threads and gain processing power in multi threaded applications.
What you loose by disabling core parking is the extra performance afforded by a single threaded application having a larger on-CPU cache.