There is a specific pleasure in a page that resists slightly as you move it, and it is not nostalgia for print. It is that a small amount of inertia gives the eye time to land.
The cost is real, so spend it deliberately
Smooth scroll takes over a browser behaviour people rely on. If you do it, you owe the user a keyboard that still works, a reduced-motion path that turns it off entirely, and no interference with in-page anchors.
Pin sparingly
A pinned section is a promise that what happens next is worth the held scroll. One per page, usually. Two if the second one earns it.
