Many people concerned with the assembly language output don't use modern languages - they use C and C++ ;) And even if the best possible machine code is produce

Many people concerned with the assembly language output don't use modern languages - they use C and C++ ;) And even if the best possible machine code is produced most of the time, which I'm not sure is actually the case, you've still got to deal with the cases where it isn't. So you need to look at the generated code to see which case you're dealing with. Also comes in handy for stepping through optimized code. (Contrary to popular belief x64 is not hard to learn, just a bit ugly. The reference manual is pretty easy to read, and the instruction list may look daunting but you'll never need to use most of it. I actually found ARM harder to deal with; the instruction descriptions in the reference manual aren't as well written.)