Study groups are commonly utilized by many students to prepare themselves for class discussion, examinations or class presentation. You can also do it to review on your weak points and learn new ideas. I myself find study group on some point a necessity to learn effectively.
In my own experiences a study group gives me a motivation to study and update my readings because most of my buddies give me encouragement. It also helps me to learn new ideas as well as important points I missed on my readings. Most of the members in my study group are very open in sharing what they know. Hence these alert me that I should update my readings so I could also share something.
On the other hand, the disadvantage of study group is the part of compelling yourself to attend to it after the class or during your rest days. Commitment among each member is an important aspect in study group. Hence you and your group mates have to set aside other activities to study together. To join a study group or not is your own choice, because there are other people who learn better when they do it alone. If you think you will be learning effectively in joining or having a group, go on and enjoy the fun way of learning.