I have long seen people recommending heatsinks to be as smooth as possible for optimal thermal transfer from the CPU to the heatsink. It’s explained that the smoother it is, the more contact there is between the two metals and avoids tiny cracks or scratches which can fill with (thermally insulating) air or worse, thermal compound which actually backfires when used in excess. I have even seen guides on manually polishing the heck out of them to a mirror finish.
If this is the case, then why is it that CPU covers usually come in brushed metal—there are plenty of visible (usually parallel-ish) lines/scratches on them. Worse, the make/model/speed/etc. are engraved in the metal. They often even have a little hole in one corner; what purpose that serves is beyond me. Isn’t it bad when it gets clogged with thermal paste?
Don’t all these defeat the purpose of a nice, smooth surface? Don’t they reduce thermal transfer and thus increase the operating temperature of the CPU? (Perhaps the effects of lapping are too little to bother with, so CPU manufacturers don’t care?)