I agree -- it's easy to think that a few percent here/there don't hurt, but there's no global context on this. Team A takes away ~4% here, B goes on to do ~3%,

I agree -- it's easy to think that a few percent here/there don't hurt, but there's no global context on this. Team A takes away ~4% here, B goes on to do ~3%, and so on and so forth. In only five of these, and consider the chains of Pythonic imports you've seen for example, you've lost roughly a quarter of your performance. (grant me an additive/compounding? nature) This is assuming that the measurements taken in a vacuum even hold up to reality. I've seen reports for misc. other things in the 20% range, so my confidence is remarkably low. I'm not against making it easier, but I don't think everyone always need to be ready for profiling. Making opting in easier lets us ignore the hand-wavy numbers. edit: To add, the simplification of this performance cost down to percentages completely ignores scale. It's a deceptive statistician's trick. Your favorite browser accidentally releasing a debug/verbose-logging version that consumed in the range of 1-10% more power globally would be significant.