Group training is beneficial in more ways than one. The first reason you might consider it is that it is cheaper than one-on-one sessions with a trainer, making it a more affordable option. It allows you to learn from each other. Watching someone else in the group perform the same exercises give you a chance to critique them and work on perfecting your own form. Likewise, they can help spot you and study your training methods to ensure you are doing the exercises correctly. Others in the group might offer up new ways of doing things or ask questions that you didn't think to ask. They may also become a friend and supporter in your weight loss journey.
Being competitive within the group training sessions can have its pro and cons. It can push you to new levels and increase your drive to lift more weight and lose more weight on the scale. It's only when the competitive drive takes over when it can cause a problem. Don't take it as an opportunity to show the others up. Also, don't take competing against the others so seriously that you would risk getting injured to prove you are stronger or faster than them.
A little healthy competition is a good thing, but be careful not to let your competitive nature take over the situation to the point that all you care about is one-upping the others your train with. Every one has different abilities, strengths and weaknesses. Doing your personal best and only comparing your progress from where you were in the past is the healthiest approach to working out in a group setting.
If you choose to train in a group setting, weight the pros and cons. Keep your initial goals in mind throughout the training sessions. If you joined in order to lose weight, increase your stamina, improve your health or bulk up, then focus on those goals and not what everyone else is able or unable to accomplish through the group training sessions.
Sources:
ACSM Stack Fitness