Online classes can be helpful if scheduling is an issue as most do not have set class times.
If you're not sure of your learning style, you may want to find out. For those who need more hands-on education, the distance involved in an online class may not work for you.
Unlike a campus-based class, you will not get as much interaction with other students and the teacher. This can be good and bad. You may find that you can overcome your shyness, but you may also find it hard to get in touch with your instructor.
The different types of classes may be greater than you can find at local colleges and universities.
Time management can be difficult if you need a schedule to keep you on track. Your motivation will need to carry you through as you may not have any enforced times to be "in class."
You will need to make sure you have a reliable computer and Internet connection, which can add to the costs of education.
You must make sure that the school is accredited with by a regional accreditation association. Without that, the class credit may not transfer to other colleges.