“There’s a module for that” is a common Drupal refrain. And it is very true. As of March 2014, there were 26,486 projects on drupal.org, of those 8,705 have a Drupal 7 release.
The question often becomes how do I know what module(s) I should use?
Not all modules are created equal. Pick the wrong module and your site might not work at all. Pick the right one and you save countless hours of development time. Plus contributed modules have the community helping find issues and solutions.