Depends on the necessity. If you really need more performance, then they absolutely matter. In general it makes sense to program for the platform/CPU, not the

Depends on the necessity. If you really need more performance, then they absolutely matter. In general it makes sense to program for the platform/CPU, not the compiler. Respect the CPU first, the compiler second. This turns into second nature just like everything else. From my experience, 99% of the people out there disagree, doing so for a good reason. They code for the compiler, not the system. When that's good enough, then that it is.