Many changes, including bug fixes and documentation improvements can be implemented and reviewed via the normal GitHub pull request workflow.
Some changes though are "substantial", and we ask that these be put through a bit of a design process and produce a consensus among the community.
The "RFC" (request for comments) process is intended to provide a consistent and controlled path for new features to enter the operative system, so that all stakeholders can be confident about the direction the project is evolving in.