Having taken a prep course, I will take the opposing viewpoint from most on here.
Clearly, a prep course is not necessary. Many people do fine without it. However, a prep course ensures that you begin studying at least three or four months before you take the test (sometimes more depending on the course). The courses also break down the material into manageable sections. Trying to figure out where to start with so many concepts is tough. Plus, they really emphasize the most tested concepts.
As well, courses offer a TON of material. Way more than anyone could possibly get through. There are many quizzes and little tests on any subject. Plus, they offer like 15 full length tests, as well as give you access to the 10 AAMC tests. Taking full-length tests was the best way for me to study, so it really helped me out.
Finally, the classes also teach a lot about strategy and how to take the test. This is not as obvious as it sounds. This was really helpful in the Verbal section. Many people struggle in that section, even if they are usually good at English. Developing strategies to tackle that section is vital.
I understand that the courses are expensive. To me, it was a good investment. Two grand is very little in terms of the price of a med education (but I do know it's a lot at a time when people don't have much money).
Again, if you can get yourself to start studying months in advance, break down the material, and develop strategies for taking the test, go ahead and not take a course. Many do well without it. However, if you are nervous about approaching the MCAT, think it would help, and have the resources to do it, I would recommend it.
But only you know yourself and what would be the best option for you.
