There is the parent's group for the school mentionnned above, my cycling club to discuss the upcoming rides/events and share pics (replace cycling with any kind of hobby you can think of), we have a family group chat with my parents and siblings, which are leaving in a different country as mine, an extended family in law group chat, comprised mostly of people living in another continent. At a former job we had a group chat that was meant to discuss anything not related to work, arrange out of office meetups. It sporadically served to share valuable information relative to work when there has been natural disaster so that people don't try to reach the office and stay at home. Much quicker than calling all employees.

Additionally whenever there is a social event a group chat is created so that people can discuss the organization, and after the event share their sentiments, pictures, videos.

It is never mandatory to participates in all those group chats but a lot of info go through them and they are usually useful. And the family group chats are great when you only get the chance to meet them more than a couple times a year.