I'm a part of a ton of Slack communities but I'm active in only a handful.
Slack works to its fullest only when it is implemented in a team and everyone's supposed to use it for communication. Slack could/should improve on making the communities on it better by adding relevant features.
As a remote designer, this is a must have. I'm always contactable and available. Super easy way to also have quick calls and communicate with other team members on different teams.