You dont mind a product which is not portable,is hard to maintain,is hard to debug is hard to optimise and in most cases cannot be worked on by more than one person at a time.Timing issues are fine if you have time critical function then use in-line assembler otherwise insisting on writing purely in assembler is a mugs game.
It can go too far the other way and I know of companies where the programmers are utterly isolated from the hardware by the super duper compiler and they don't even look at the output to see what it has made of their super duper code.