The importance of RFCs has been emphasized by many people. As @tison said in How to Participate in the Apache project community:
A description is certainly needed for any non-trivial change to explain the motivation. For major changes, design documentation becomes even more necessary since no one has a permanent memory, and people always forget why they did something in the first place. The precipitation of design documentation plays a vital role in freeing the community from the uncertain evolution of human activities.