The operative word was always "premature". As with everything, whether or not a particular optimization is worthwhile depends on its ROI, which in the case of

The operative word was always "premature". As with everything, whether or not a particular optimization is worthwhile depends on its ROI, which in the case of software depends on how often your code is going to be run. If you are building a prototype that's only going to run once, then the only optimizations that are worthwhile are the ones that speed things up by times comparable to the time it take to write them. On the other hand, if you're writing the inner loop of an LLM training algorithm, a 1% speedup can be worth millions of dollars, so it's probably worth it even if it takes months of effort.