I suspect that by the time I see the changes in the assembly I've forgotten what the previous assembly was (I don't have eidetic memory). I'd like this sort of rapid >change>optimized asm with code interleaved and aligned diff's>repeat iteration cycle for learning purposes. I long ago wanted to learn some asm but not having such ability makes it too tedious process. Hard to say how much use would it be for performance optimization - perhaps after I knew some asm through the rapid change iteration then I could use it to see if there's something slow going on.
Of course that sort of facility would ideally work not just in C# but in C++ too.
btw. Quite interesting read from someone claiming to have eidetic memory. Particularly the rough statistics bit. http://www.quora.com/What-is-it-like-to-have-a-photographic-eidetic-memory