Earlier quoted context omitted.
If you need smooth scroll you can't rely on browser support and need to use a library or cook something up yourself. It's surprising how few browsers work with smooth scroll. Today it's basically only Firefox; not even Chrome.
What web page or application would need smooth scrolling? What can't work with whatever scrolling is normal for the browser/OS/hardware? Looking cool at the request of some manager does not constitute a need.
Done right, animation isn't just snazzy, it produces a more usable, more approachable user interface. It helps the user keep a good mental model of what's going on. It's easier for them to mentally track "ah, when I select this item, it also selects that other item in the other list".
It's the same reason why when you click an app on your phone it animates up from the app icon when the window opens. The animation wordlessly tells the user "I'm opening this app, and the window that's appearing is born of the icon you just clicked." Necessary? Not exactly. More natural? Absolutely. Nothing just snaps into existence in the real world, except for maybe things like lightning.
When things appear out of nowhere it can be jarring. Animation is especially called for when it might not be intuitive why you're making a change to the visual state, or when you want to call attention to something.
Keep in mind that a generation ago, pretty much every piece of software (even games!) came with a printed manual that the user needed to read first before expecting to be able to accomplish anything. Today users expect to be able to figure things out for themselves, and animation is part of the user experience that helps users learn their applications naturally by exploring the user interface.