What are the JPA @Table annotation "catalog" and "schema" variables used for?
Catalogs and schemas are "namespaces" that you define on the server side of the database. Some databases contains schemas, some contains catalogs, and some contains both. When logging in with a specific user, some databases defaults the schema/catalog to the user's namespace, causing the table to not be visible to other users, thus, causing the need to use a "common" namespace. So, depending on the database you are using to back your data, you might want to ignore those settings.
For MySQL, you might want to ignore those settings. This is because the "database" part of the JDBC URL (the one after the last slash) points to the database name, which is semantically identical to schema (for MySQL).