No The box ought to remain "unchecked" if you wish to have possibly related posts to display. That being said do note that there are not always possibly related posts available for display. Also note that the data comes from a widget and all data in widgets is cache and that means there can be time delays until a display appears.
Setting that issue aside you have a much larger issue to address. You are inadvertently "spamdexing" ie. overusing tags and/categories. If you have heard that "more is better" that's utter nonsense. "Less is more" applies to Categories and Tags. We use only the minimal number of relevant Categories and Tags on any post. See here please > http://en.support.wordpress.com/global-tags/#missing-posts