Suppose you are on a page with a long paginated table (may be per page 500).
Then you scroll to the bottom to click the Link and go to the Next page.
If there is <Link preserveScroll /> then, in the next page i.e. /users?page=2 the scroll position will be preserved (i.e. you will ideally remain at the bottom of the page).
If there is NO preserveScroll, the next page /users?page=2 will automatically send you to the top of page (like default browser behavior when clicking <a href />).