Well, I'm not too sure. The CM690 and some other case vendors are pressing holes and allowing fan mounts for the rear of the case. It takes a thin fan, but it's there.
I think they just saw that the spot was hot and figured "why not?". It's really iffy since it's probably just conducted heat and blowing air on a metal plate or bare silicon isn't going to do much anyway.
You can do it cause it shouldn't hurt one bit...but clean up your shavings well. A magnet while doing the job helps a lot.
My spedo has room for a standard 120mm fan behind the CPU area
not sure what to do with it. right now, there is a thermal probe there.