If you're not developing for a real-time system, like most (all?) larger games or software for embedded hardware, it is likely that you are not thinking about performance very much, even if you have the time and skill to do so.

You don't think about performance, as a developer, usually, until it becomes a problem, and there are so many layers and frameworks between an MP3 player and the CPU that this kind of thing should be expected.

It is much more difficult to keep a real-time system working in real-time than it is to keep something performing as well as a desktop computer user expects it to perform.