Snowflake schemas normalize dimensions to eliminate redundancy; that is, the dimension data has been grouped into multiple tables instead of one large table.
For example, a product dimension table in a star schema might be EDW 3NF into a products table, a product_category table, and a product_manufacturer table in a snowflake schema.
While this saves space, it increases the number of dimension tables and requires more foreign key joins.
The result is more complex queries and reduced query performance.