Fitness classes not only offer physical benefits, but also the social factor in interacting with other participants. You get the support and motivation from the instructor and the other participants in the class to help you along the way too.
You’re also more likely to stick to your exercise routine and achieve your goals if you work out in a group environment. Great music, an instructor with a great personality and working out with other people is FUN! If you didn't have fun in a class, then go to a different class that suits your personality better. It is trial and error to find your perfect class, but once you find it you'll love it!
Plus, with the variety of classes, you will never get bored of your fitness regime with the variety of exercise choices offered in group settings.