Also, just having a standardized way to do a lot of things. One such example is menus. Just about all Mac apps — even ported stuff using third party UI toolkit

Also, just having a standardized way to do a lot of things. One such example is menus. Just about all Mac apps — even ported stuff using third party UI toolkits — hook into the standard menubar APIs, which means that every menu item of every app can have a key shortcut assigned (or reassigned) in System Preferences, even when the app's dev never bothered to add such configurability. Similarly, accessibility and scripting APIs can reliably grab the menu items of any app, improving automation and interoperability. One could probably even write a full replacement for the macOS global menubar without much fuss. Compare this to Windows and Linux where it's quasi-normal for apps to implement menus their own way or eschew them altogether — there is no single way to grab menu items, just a ton of different possible ways, and if an app dev has decided to do their own thing you're just SoL.