Assigning a user default permission ("Read") to a warehouse in a Fabric workspace enables them to connect to the SQL analytics endpoint, which is the equivalent of CONNECT permissions in SQL Server. However, this permission only allows them to connect; it doesn't grant them the ability to query tables, views, functions, or stored procedures within the warehouse unless they're also given access to those specific objects through T-SQL GRANT statements.
In essence, the default "Read" permission provides the necessary connectivity to the warehouse's SQL analytics endpoint, but it does not automatically grant access to the data and objects within the warehouse itself. Further permissions need to be granted through T-SQL or Fabric's workspace roles and item permissions system.
Reference:
https://learn.microsoft.com/en-us/fabric/data-warehouse/share-warehouse-manage-permissions