The new features will improve search results in a Google custom search engine for your site if you utilize sitemaps:
Custom Search is built on top of the Google index. This means that all pages that are available on Google.com are also available to your search engine. We’re now maintaining a CSE-specific index in addition to the Google.com index for enhancing the performance of search on your site. If you submit a Sitemap, it’s likely that we will crawl those pages and include them in the additional index we build.