Community energy has two main characteristics:
1. Energy is produced locally
2. People make decisions about it (e.g. what is done with profits) by consensus
Typical energy production in the UK is usually privately-owned, large scale, and transported to distant places via a centralized grid.
Producing energy locally overcomes several issues: high energy prices from energy companies driven by profit; having no control over our energy supply (such as in the face of a natural disaster); and the inefficiency of transporting electricity via a centralized grid (electricity is used up with distance travelled).
In short, it makes sense for the people using the service to be in control of the utility, rather than a privately-owned company motivated by profit margins.