Check out this awesome post by AJ Kohn
To answer your question...
"What I’ve observed over the last few years is that pages that haven’t been crawled recently are given less authority in the index. To be more blunt, if a page hasn’t been crawled recently, it won’t rank well."
"The pages that aren’t crawled as often are pages with little to no PageRank. CrawlRank is the difference in this very large pool of pages. You win if you get your low PageRank pages crawled more frequently than the competition."