On-line learning is beneficial for many reasons. First, those who do not have time to actually go to a campus benefit by being able to complete their coursework on-line. Another benefit to on-line leaning is that it can allow a person to move at a slower pace if needed (within the constraints of the class and instructor--if attending on-line classes).
That said, many on-line classes (especially Master's level classes) are very challenging. These classes require the student to take control of their own study skills (essentially, it can help with focus and time management).
With on-line learning, more people have access to colleges and universities (given the have on-line programs) that they would not be able to attend. Essentially, a campus grows exponentially when on-line classes are offered. By offering on-line classes, colleges and universities can expand their student body as well.
Outside of that, some students (or even people who are no longer in school) may choose to learn things on-line which they could not do in a classroom. Some people learn languages on-line, how to do things (as seen in "how-to" videos), and can even learn to play musical instruments (all in the comfort of their own home).