Online courses let you "go to class" at the best time of day for you. You can often work at your own pace, except for adhering to certain instructor-imposed deadlines. Traditional courses don't offer this flexibility; you must learn new material whenever the class meets.
If you are an auditory learner, prefer live interaction with instructors and classmates, or if you like to ask questions and receive answers on the spot, then face-to-face classes may serve your needs better.
Online courses typically will cost you less. You don't have to pay for gas, parking, and sometimes textbooks. You also don't have to pay for meals on the go.
Online courses seemingly limit communication with your professor; however, most instructors are available via email and online message boards. If you are shy or simply not the type to raise your hand in face-to-face class, online courses may actually allow you more individual contact with instructors.
With online courses you must be disciplined and manage your time well; without self-motivation you can easily fall behind.