I would like to have seen a section for when continuous integration is NOT needed, and would be overkill. For example, I have a solo project where my workflow is: make changes to code, run the test suite, fix any failures that come up, and then push to heroku. I tried CircleCI but I found that the only benefit it offered me was offloading the testing and deployment to another environment. In some ways it actually complicated my workflow, not simplified it.
You're right; CI is pretty much a waste for a single person dev shop. But it's a godsend when working on larger projects: it centralizes processes that should ideally happen automatically, and increases developer confidence in the quality of the codebase by removing the deployment variables from the situation. Any team working on a reasonably large project should be using CI in some form.
For example, if you have a staging environment, and a developer pushes a change to that environment and wants you to make changes and test against his changes, you have to coordinate the deployment to make sure you don't overwrite his changes and vice versa. With CI, all check-ins would get automatically deployed to the staging environment using static scripts, so every deployment is exactly the same. It saves a lot of developer time, and removes the "which developer is a better sysadmin" variable from the equation.
