DrupalCons are not only a great place for sessions and parties, they also provide a great source for training, "Birds of a Feather" sessions, general discussions and sprints.
Let's illustrate the power of the latter: Sprints mostly happen in a large room with a lot of working space, fast internet and enough power. The Drupal community leverages the opportunity of having so many people working together, in person, to accomplish things that would be more difficult to achieve while collaborating online.
The biggest sprint at DrupalCon usually takes place on Friday. This year there were over 400 Drupalistas working together on Drupal 8 and other topics such as documentation, usability, contributed modules, etc.
There is also an initiative called "Get Involved with Core", which helps beginners contribute to the core of Drupal. Because many beginners think that being a core contributor means you need at least five years of experience with Drupal, this is a great opportunity to show them that this is not the case. Of course there is a lot of deep and interminable discussions, but there are also many issues which are easy tasks for beginners to start with. Check out the novices issues here.
A tradition which evolved in the last few years is that Drupal creator, Dries Buytaert, commits a patch directly on stage at the sprint. Last year at DrupalCon Denver he committed a patch which was contributed by Kathryn and me.