On most situations (blog, forum, thread view) a user most likely goes to either the first or last page and stays there. He will not click on other pages within this context (page 2,3,4 ...). A YUI Paginator integration would be great but not necessary.
However when a user goes to any other page than the first or the last, he will more likely go to other pages. In these cases, it makes sense to integrate the YUI Paginator for quicker browsing. In case he goes to page 2, these would be the pages 1 and 3. In case the user browses the second last page, the last page should be included in the paginator.
If content would only be loaded when clicking on the pages, a paginator integration would not have to think about the above points.