In many cases you need to train in a group, to get help in some physical activity since the person in your training can increase more weights in most of the exercise, above all the help is needed as a check in case you want to stay without completing your complete repetitions and you are going the weight asia you can or not ocacionarte an accident, it helps you more in those things when entering into group.
Most of the times that you train in the gymnastics group the person feel great in this regard because it inspires you to train stronger by getting better results, since people mostly take physical training as a competition and are always comparing themselves among them in their physical layer, but that everything is a fun to train in that group way.
To train only in a physical activity is different but above all in the gym, you are limited to lifting weights in some physical activities, especially in the exercise of pre-bench weights there is need help from other people if you are going to lift more weights than control your body, since if it does not require that help your evolution is developing in a slower process in grabbing to gain more strength in the body. Also training alone is boring almost always because it takes the amino of other people to not rest much in training and also it takes people who encourage you to do all your exercises demanded in the day, to be able to finish the physical training completely.
If training in a group is very good, because if you need an exercise to finish the other partner or friend encourages you looking for the way to finish this physical training, at least that most of the group does not want to continue training because exhausted that are still so there is always one that ends up encouraging the group to make sure that the whole group finishes with all the physical activities, until all are satisfied with its efforce.
And autedes of this public comment as he likes to train, specify and correct me if I am wrong about something.