if you are an expert or a passionate person with a respectable amount of knowledge in your field, there is a huge amount of people around the internet that are in need for your knowledge to either start their career or become better performers at their current ones. Or, to just learn something new that it can end up to be their lifetime passion!
If you are good enough to market for a course or a training of your own, you will notice a big demand that can reach a point where you have to limit the number of attendants. Depending on what you exactly are teaching, you can however guarantee yourself an extra income or even shift to a full-time trainer/teacher.
Teaching or training in general will open up a big door of opportunities ahead, because of the amount of liberty you will get the second you finish setting up your programs and then focus only on repetitive minimal tasks. Keep in mind that when each new training occurs with new students you raise your chances for more publicity to yourself.