Namespaces are virtual clusters backed by the same physical cluster. It's the first level of isolation between applications.
When to Use Multiple Namespaces⚑
Namespaces are intended for use in environments with many users spread across multiple teams, or projects. For clusters with a few to tens of users, you should not need to create or think about namespaces at all. Start using namespaces when you need the features they provide.
Namespaces provide a scope for names. Names of resources need to be unique within a namespace, but not across namespaces.
Namespaces are a way to divide cluster resources between multiple uses (via resource quota).
It is not necessary to use multiple namespaces just to separate slightly different resources, such as different versions of the same software: use labels to distinguish resources within the same namespace.