What exactly should a robots.txt file say if you want your whole site spidered 24hours a day 365 days a year?
then you have an EMPTY robots.txt because in robots.txt you EXCLUDE folders or DENY access to particular or all bots. if you love to be indexed by all you may add the new LINE Sitemap: /sitemapindex.xml STUDY (Google) what belongs into that file Sitemap: /sitemapindex.xml and in what format. its used to announce to ALL SE's where your site map files and RSS feeds can be found
In robots.txt file you can exclude your folders that you want that crawler should not crawl the site It is a good parctice to add the robot.txt file in you site so that the bandwidth of the site will not waste