The Published flag (is_published resource attribute) was introduced along with the Advanced workflow implementation years ago.
As explained in the documentation, this flag combines with the RESOURCE_PUBLISHING and ADMIN_MODERATE_UPLOADS settings to decide whether resources will be visible users based on this flag.

In brief, if RESOURCE_PUBLISHING is turned on, any new resource will be configured as unpublished, and it won't be visible to users (except Owen, group managers, and admin) until the Published flag is not turned on.

However, the Published flag confuses users, since many of them expect it to have an effect even outside the Advanced Workflow. The expected behavior is to hide the resource from the catalog when is set unpublished, independently from the advanced workflow scenario.

The option of hiding a resource from the catalog can be useful in several cases. One, for example, is disabling a resource when queued for deletion.

Notice that this Publishing has a stronger effect compared to Advertized. When set not advertised the resource is only hidden from listing and searches, but users can still access the resource directly through other resources (Dashboards, Maps, etc.).
When the resource is not published it will not be reachable at all, with a similar effect to a private resource (share permission set to None for everyone).