Think of Data Catalog as a metadata as a service, it's serverless and requires no infrastructure to set up or manage.

Cloud Data Catalog provides discoverability of labels, which helps managing complex resources or cloud billing.
Those labels have to set manually for example in BigQuery where labels can be added to datasets, tables, and views.

It provides metadata management services for
cataloging data assets via custom APIs and the UI,
thereby providing a unified view of data wherever it is.

It supports schematized tags like enum, bool,
or datetime and not just simple text tags,
providing organizations reach
an organized business metadata.