Nowadays, more and more people are exercising in groups, but there are people who prefer to do it on their own.
The are a number of benefits to exercising in groups. In the first place, it motivates people to attend. This means that there is less excuse to stay home. In addition, you can meet new people, for instance, you can chat and dance with others.
On the other hand, there are a number of disadvantages against. Firstly, there is less individual attention. This way, the instructor might miss mistakes. Secondly, there are people at different fitness levels. Consequently, not everyone can follow the class pace.
As far as exercising is concerned, I think exercising in groups is good because you can get fit and meet new people at the same time.