A very important point in Search Engine Optimization is to be sure that search engines crawlers can access all of your blog pages and posts, so they all can be indexed. There are many ways to make sure that all of your pages and posts can be accessed by crawlers, such as creating an archive page template. Therefore, the best way to guarantee that crawlers can see and index all of your site pages is to use a sitemap.
According to sitemaps.org,
Sitemaps are an easy way for webmasters to inform search engines about pages on their sites that are available for crawling. In its simplest form, a Sitemap is an XML file that lists URLs for a site along with additional metadata about each URL (when it was last updated, how often it usually changes, and how important it is, relative to other URLs in the site) so that search engines can more intelligently crawl the site.
In other words, using a sitemap doesn't guarantee that absolutely all your pages will be indexed by search...