With shadcn / the copy paste format, you’ll almost never see that happen. The button shadcn provides for example is just css / tailwind. And if you did ever for some reason want to bring in a dependency for your button component you wouldn’t have to consider its effect on your other UI elements. The rest of your components can live independently (for the most part)
We have customized UI components we got from shadcn and now some use radix and some use base ui, and some have other dependencies or no dependencies at all. Properly tree shaken this is not a big deal at all and we can upgrade components individually as needed.
For boring applications this may be a bit much. But even then if you wait too long and mantine falls behind more than a couple versions, who knows how easy it would be to get your whole project up to date.