If you're a driver, at some point you'll probably need to write bytes into a device register, mapped to a raw address in physical memory. That's a fundamentally unsafe thing to do: it relies on you as a programmer setting up the structure of the data in those registers correctly. Get it wrong and you can scribble over some arbitrary piece of memory, for example. The compiler can't check your working. It doesn't know the specification of every piece of hardware - that's what drivers are for.