With all the goodies, there are bound to be a few flaws. The major flaw being that a student cannot get a one to one correspondence with a professor in the correspondence courses. All they get is printed notes or online material, which they can print for further use. The interaction with professors, which can help get rid of the doubts in the content, is totally absent here. This can cause a problem if your exams are nearing and you come across a difficult problem just a few hours before the exam. In the regular batches, you can take the contact numbers of the professors while interacting with them and this helps you to further increase your contacts.
In the correspondence courses, you have to study alone and not in a group. This can be a disadvantage as in regular courses; you at least have some one studying with you and do not get bored. Studying alone can be boring and tiring sometimes and you start losing interest to study further. Only the motivated people persist with these kinds of courses and this leads to a high dropout rate in these courses. Further, you lack a sense of competition when you are working alone and this may lead to a not so good future, where competition can be dangerous and only the fittest are able to survive. So it is better if you enquire beforehand to someone who has already taken the course, while registering for that particular course.
The final disadvantage is that you have to pay the entire fees of the course at the time of enrolment and this, in most cases is non refundable. This can be a problem if you are not satisfied with the content provided by the institution that offers the course. This can be a loss of time and money.