I think mostly because having scads of clever conditionals all over the place greatly increases the risk of subtle and hard-to-reproduce bugs. From a 2007 Carma

I think mostly because having scads of clever conditionals all over the place greatly increases the risk of subtle and hard-to-reproduce bugs. From a 2007 Carmack email [1] : > The way we have traditionally measured performance and optimized our games encouraged a lot of conditional operations -- recognizing that a particular operation doesn't need to be done in some subset of the operating states, and skipping it. This gives better demo timing numbers, but a huge amount of bugs are generated because skipping the expensive operation also usually skips some other state updating that turns out to be needed elsewhere. > We definitely still have tasks that are performance intensive enough to need optimization, but the style gets applied as a matter of course in many cases where a performance benefit is negligible, but we still eat the bugs. Now that we are firmly decided on a 60hz game, worst case performance is more important than average case performance, so highly variable performance should be looked down on even more. There was fascinating breakdown [2] of a single GTA V frame about five years back. It was a real eye-opener for me - whole full-screen rendering passes for things like water reflection and refraction when there isn't even any water visible in the scene. [1] http://number-none.com/blow/john_carmack_on_inlined_code.html http://number-none.com/blow/john_carmack_on_inlined_code.htm... [2] http://www.adriancourreges.com/blog/2015/11/02/gta-v-graphics-study/ http://www.adriancourreges.com/blog/2015/11/02/gta-v-graphic...