Drupal camps are different from DrupalCons in several very important ways. I helped organize DrupalCon San Francisco in 2010, and I've been an organizer for BADcamp since 2007. BADcamp has been growing in size each year, but I still want to voice what I think the key differences are between camps and cons.
What makes Drupal camps different from DrupalCons, and why are they a necessary part of the Drupal community?
Drupal camps are usually cheaper than DrupalCons. This means that camps will draw a slightly different audience. The cheaper events attract more non-profits, educational institutions, hobbyists, new-comers, and people who are curious about Drupal but may not be ready to invest in an expensive conference ticket. In the case of BADcamp, our event is completely free.
Drupal camps are usually smaller than DrupalCons.
DrupalCon has grown to be a very large event with a very, very large budget. Camps are usually much smaller, and can be executed on a tight budget. In addition to having a more reasonable budget (an advantage for organizers) a smaller event can also benefit attendees. Having fewer people present makes the event feel more personal, and allows for accidental meetings with the Drupal-famous. Realizing that your favorite core contributor is a also friendly person is truly priceless.
Drupal camps happen at lots of different times and at lots of different places.
This means they are more easily accessible to almost anyone. DrupalCons happen only twice a year, can conflict with schedules, and can be very far away. Having a camp in your own backyard means that it's easy for you to get involved with the community, on your own terms. You don't need to fly half way around the globe to talk find out what's cool in Drupal or to share your thoughts and opinions.
Last but not least, camps tend to be organic.
Each camp is born from its own local community, as an answer to the needs of that community. This allows each one to be a little different, and include the activities that are important to each community. There's no decree from the Drupal Association telling camps what needs to be included to make a camp successful, and this allows freedom, creativity and innovation. These are qualities we see in the Drupal project itself, and I'm happy to see them reflected in how the community gathers.