There are several reasons why groups are formed, including: 1. Locality or geography, as people join groups in their local community where it is convenient, such as a local soccer team, where social benefits come from friends also participating. 2. Shared interests or common goals, as groups form around a particular interest or talent like a hobby or sport, or to achieve a common goal like a church or fundraising group. 3. Specific needs, with groups forming temporarily to meet a need, like a volunteer group after a disaster, or more permanently around an ongoing need like a playgroup for children.