Here’s the idea: if you complete a task, you get paid for it and move on to the next one. If you complete a task and write down what you learned on a public blog, you at least get some residual page views that you can monetize. Any individual post will likely not make much, but, like in Calculus, the sum of a lot of small actions can add up to something meaningful.
As a side effect, building a popular blog can help you come up with additional revenue streams: contract blogging, SEO consulting, etc. Sometimes, you don’t need to do extra work, you just need to leverage your existing work.