When you are shipping binaries, you usually do not have control over the cpus your users are using. Setting march/mtune to native breaks if the developers machi

When you are shipping binaries, you usually do not have control over the cpus your users are using. Setting march/mtune to native breaks if the developers machine is noticeably newer than the users machine. Also letting the build machine configuration decide which level of simd to target is too flakey, so most software specifies the target explicitly.