The problem with this was expalined a while back when Costco had to recall butter because the packaging didn't say it contained milk. Sure someone who's deathly allergic to it will be careful, but these lists are more or less blindly get inputted into other systems. You'd be surprised how many businesses buy from Costco in bulk.
Eh. That's like saying speed chess "is not at all comparable" to chess. There's differences but it's the same game. In this case speed coding still relies on the programmers understanding of the problem. There's just usually less edge cases that you have to handle (usually input can be read in a less safe way because it's in a specific format, and others)
But to be specific, it's not like some program that was in the old windows partition would suddenly start executing on your system anyway.
BUT someone who steals/searches the laptop can see that partition's contents (for the bytes not yet overwritten) and recover files, directory listings, etc. which may tie that laptop to its previous owner.
So if the car gets in a crash you can be standing up and unsecured!