Simulation games like Factorio, Rimworld, Kerbal Space Program, Dwarffortress etc use 100% of single CPU and <10% of others. In factorio, I can make ginormous factories that are bottlenecked by a single CPU. Sometimes say my factory produces X rockets per game-minute. I make a bigger factory that produces Y rockets per game-minute where Y >> X but since now CPU cannot handle the load I now produce <X rockets per real-time minute. So making my factory bigger was a net negative in terms of rocket per real-minute.