Definitely need to optimize a bit for games and huge scale web apps. We've been finding big optimizations in our app recently. App works without them because we can scale horizontally but cutting CPU usage by 30% by eliminating redundant work and reducing copies of big objects? Why wouldn't we want to do that? This isn't even fancy algorithm stuff, mostly just shoddy initial implementations by 100s of eng working on a codebase over 7 years (not even that old). Stuff like that creeps in.