not2easy - 4:09 am on Sep 28, 2013 (gmt 0)
Your robots.txt file is where you list the files and folders you do not want crawled, and also where you list the location for your sitemaps to tell robots the pages you do want them to crawl and index. It is your tool to tell robots what you want and don't want them to do on your site. Good robots will generally follow your rules, though they are known to forget them when they follow links. Bad robots ignore your rules and do as they please. It won't break your site if you don't have one, but there is little chance that robots.txt has much to do with getting you "blocked" (or unblocked). If you believe your site has been given a manual penalty, that information would be available to you in your Google Webmaster Tools account.