Yes, but it's nice to be able to predict what your compiler of choice will do, or at least to know that all of the things it might do will have similar performance. When you depend upon certain optimizations, you need to diagnose the compiler's failure to do them. This usually means knowing both how to read assembly, and how to force the compiler to do what you want.

This doesn't matter when any correct program is "good enough," but it matters a whole lot when failure to perform specific optimizations makes a program unacceptably slow.