According to a Kristv.com article, there are five types of people best suited for online learning. Among them: the traveler, the business person, and the homebound. Here's a blurb from the article:

"If you frequently travel abroad, are constantly on the go because of business, are enlisted in the Armed Forces, you or a loved one has a physical or health disability, or you live far from a college campus (or just can't get to one near you), eLearning may be the best bet for achieving your higher education goals."

While a person's current activities may make online learning a more convenient choice, I believe that personality traits are the better determiners. A person who is organized and self-motivated is far more likely to succeed in an online course than one who needs constant encouragement and supervision.