Managing a website without documentation is like trying to put together Ikea furniture without the directions--it's just not happening. Often, documentation is overlooked by companies and organizations on a budget, but it is a truly invaluable part of building a new website.
When you first install Drupal, you are given a lot of power. With all of the contributed modules available, you can do pretty much anything.
With Drupal 8 in the final stage of development, support for Drupal 6 will soon be coming to a close. If you are currently running a Drupal 6 site, now is the time to start thinking about upgrading, and choosing which version of Drupal is right for you.