Hi Srishti, A bit of self-introspection on this topic might result in self-realization on whether you really need coaching for GMAT. While there are no perfect answers to this (and no studies available, which show whether people who do self-study fare any better or worse than people who join coaching), it is really an issue that is very subjective.
Following are some of the points that will work for you if you join coaching. If none of these points resonate with you, then chances are that you do not need coaching:
1. Speed up the on-boarding process: If you are starting cold, then chances are that you would spend significant amount of time to just get into the groove and understand how to get into the thick of things. This would include getting a hang of the exact structure of the GMAT, knowing the best practices, and appreciating the dos and don’ts. A coaching institute would obviously have all these laid out for you.
2. Study Resources: As opposed to most other exams, GMAT suffers from a problem of plenty. If you look for GMAT material on Google, you will literally get millions of hits, and GBs and GBs of data available for "free" download. Unfortunately, most of the material that is available on the net for free download, is neither authentic not representative of the actual questions on GMAT. For unsuspecting students who are self-preparing, chances are that they would burn their fingers a few times, before realizing the sanctity of authentic study-material for GMAT. If you join a coaching institute, then obviously the institute would ensure that you have firsthand access to the best study material.
3. Instructors: Passionate and genuine Instructors of GMAT can make every dollar and every minute of yours, worth the experience. Teaching for GMAT for years, these instructors thrive in explaining the concepts to the students in an extremely articulate manner. If you do not join a structured coaching, then chances are that the learning curve will be slightly more elongated. However, if self-learning is something that has always worked for you, then perhaps this is a point that would not appeal to you too much.
4. Support outside the classes: Apart from the classes, coaching provides an invaluable support with concepts and doubt clarification all through your GMAT journey. In the current scenario, there actually are some good freely available support forums (such as BeatTheGMAT and GMATClub) available for students. These support forums can actually act as substitutes for "outside the class" support that coaching institutes provide. However, since these GMAT forums are obviously available to public at large, you have to be extremely judicious in terms of filtering out the advice and the solutions that people offer on these platforms.
5. Structured approach: The kind of material that you need to get access to, the sequence in which you should be studying the various concepts, and the best sources of those concepts are few pieces of the GMAT puzzle that coaching centers would have solved for you.
6. Discipline and group-study: Classroom coaching, by its virtue of fixed timings, rigorous schedule, and predefined pace, would necessitate that you are disciplined in your preparation. It would also give you a group-study environment, wherein you are likely to find students who are as committed to making it work, as you are. On the other hand, if you feel extremely self-motivated without any external intervention, then this benefit of the coaching classes would not appeal to you.
So, there you go, based upon the above points that come to my mind right now, do a self-introspection and decide accordingly. Before I end, if you do decide to opt for coaching, an earnest piece of advice would be to attend a free trial class with at least few coaching institutes or online coaching classes, before you finalize one.