It will both consume less and also produce less head, thus allowing you to overclock a little further.
On my i5-750, for example, I've got a profile that disables 2 cores and I can get an extra 200mhz out of it and this profile is specially for when I'm playing crysis, which only uses, as most games out there, 2 CPU cores.
Do it, all the way, specially if you can easily switch between profiles on your motherboard setup.
Also, once I've disabled 3 cores but one to overclock the hell out of it under air and bench with the single threaded super pi
by the way, the part that heats the most in a core, if I'm not mistaken, is the cache. So, if you have two cores that shares a same cache memory, you should disable those, to completely disable their cache and get even lower temps ( I don't really know how your processor's architecture is, so maybe it's better to just disable the cores that fail first at prime 95, for example. I don't know if you noticed, but sometimes one of your cores can fail within 2 hours of testing and the others can go 20... that really pisses an overclocker. I wish we could set different voltages for each core. It sucks to increase the voltage for all cores when only one is failing.)Edited by EduFurtado - 11/4/11 at 4:04pm