Asynchronous and synchronous learning refers to two types of online classes. Synchronous classes are those that require a designated login at regular times at the same time as the instructor and other students, similar to attending a face to face class. Asynchronous classes don't require a live login time. These classes are conducted via email, discussion groups and forums.
Clearly the big advantage of asynchronous learning is the opportunity to "attend" classes at a student's own convenience. This is an important factor for people who work full time or have family obligations. It also allows a student to learn at his own pace an in a way that suits his individual needs and is a form of collaborative learning that shifts the focus from teacher-centered to student-centered with the teacher as facilitator to student interaction.
The lack of a structured environment can be a big drawback for someone who needs it. The minimized teacher presence can also be a hindrance for some students, potentially leading to severely decreased feelings of motivation and involvement, and thus negatively affecting the learning outcomes. Another problem is the unpredictable amount of time it can take to receive reactions and feedback and the lack of visual and aural cues is also a potential drawback for certain types of learners.
Times of economic downturn are historically good for education when people are stimulated to return to school as a result of limited job opportunities or out of the need to gain new skills to advance in their fields. The economy is also a factor in asynchronous learning as gas prices climb because higher fuel costs lead to students choosing online education formats. Overall online education is positively impacted by bad economic conditions, in turn having a positive impact on the economy.