Last updated 7 September 2016.
People around the world contribute to Drupal for all sorts of reasons:
More contributions mean less work—for others and for you. When you write a docs page or answer questions, you invite others to respond with their own helpful comments—and your words become part of the conversation that steers the Drupal project. When you contribute code to Drupal, you don't just help others—you invite them to test, repair, improve, maintain, and document your code along with you.
Contributors have a stronger voice in the project. Those who build, write, teach, communicate and organize Drupal events and contribution sprints have greater influence on the future of Drupal.
Contributing helps you learn Drupal faster. Nothing will improve your understanding of Drupal like explaining it to someone else—or taking pieces of it apart and fixing them.
More contributions mean more business. Your contributions to the Drupal project are public. Clients, customers, employers, and contractors around the world can learn your name and admire the evidence of your Drupal skill.
Drupal community members are good people. Developers, designers, site administrators, writers, students, project managers, business owners—the Drupal community is filled with talented and enthusiastic people, most of whom enjoy working with others like themselves. Contributing is a great way to show your skills and your interests—and to initiate conversations with the community members who share them.