Comment by Earw0rm

Optimise is never a neutral word.

You always optimise FOR something at the expense of something.

And that can, and frequently should, be lean resource consumption, but it can come at a price.

Which might be one or more of: Accessibility. Full internationalisation. Integration paradigms (thinking about how modern web apps bring UI and data elements in from third parties). Readability/maintainability. Displays that can actually represent text correctly at any size without relying on font hinting hacks. All sorts of subtle points around UX. Economic/business model stuff (megabytes of cookie BS on every web site, looking at you right now.) Etc.