My 1st post!
It may have been answered here multiple times. Sorry if that's the case. I haven't found it. Here goes:

What's the purpose of the finned aluminium heatsink used in the J-head style of 3D printer ?
I know you need to get the filament very hot to melt it, but why cool it down just before heating it?
I can imagine a few vague reasons why, but nothing definite enough to be sure.

I asked a (Chinese) seller of the part, on ebay. I asked in plain English, but they don't understand me.
I asked an Australian seller (I'm in Australia) of the part on ebay. He wasn't sure either.

Thanks
-Joshua (nickname: Dodgy)