The class will be there when the student is ready. That's a wonderful advantage to those with full time jobs, full time families, transportation problems, special needs or interests. One must log on and be prepared to read through many pages and comments. They have definite start and stop dates, many with assignments due weekly. A great deal of time is spent visiting web sites, reading articles, dealing with technical problems.
Technology can be unreliable.
The plan to submit homework at the last moment can be defeated with a busy or down server. Sometimes the 'cyberdog' eats your homework. You should always have a copy saved to a disk or a hard copy so you can resubmit. Failure to have a copy leads to more work. Most people who have taken online courses find them 'labor intensive'.