You can code in binary, but the only thing you'd be doing is frustrating yourself. We did it in the first week of computer science at the university. Assembly is basically just a human readable form of those instructions. Instead of some opcode in binary you can at least write "add", which makes it easier to see what's going on. The binary machine code is not some totally other language than what is written in the assembly code, so writing in binary doesn't really provide any more control or benefit as far as I'm aware.