The whole point of Unity Catalog is that you can share it between workspaces. It sits at the account level, and you assign workspaces to it from the Account Console (or script assignment through Terraform or similar technologies).
The beauty of Unity Catalog is that you can share the same data between workspaces hassle free, and you can secure the objects (catalogs, schemas, tables, etc) which means you will have 1 place to do governance, instead of having to replicate it for each individual workspace (like you'd have to do if using the classic hive_metastore). This means that if you write data to a UC table from workspace1, it will immediatly be visible in workspace2, and vice versa.
Unity Catalog metastore also uses a data lake for default storage, which you create and control in you cloud provider. This means you have way more flexibility in setting up security on the storage, which you don't have if you are using hive. Hive uses dbfs, which is not secure by any means, and should not be used for storing sensitive data.
