Then again, 'reasoning about it' can easily go awry if your knowledge doesn't get updated alongside the CPU architectures. I've seen people confidently say all sorts of stuff about optimization that hasn't been relevant since the early 2000s. Or in the other direction, some people treat modern compilers/CPUs like they can perform magic, so that it makes no difference what you shovel into them (e.g., "this OOP language has a compiler that always knows when to store values on the stack"). Benchmarks can help dispel some of the most egregious myths, even if they are easy to misuse.