In database design it is in consistent form. So when the database is designed only relevant and required data will be stored. Because of that the layout of the table allows the data to be consistent. In the other hand to keep the data consistent this can be handle through implementation of primary keys and unique key constraints.
Also overall performance of the application is also dependent on the design of the database. Not only that, database design improve the store and management of data and its structures. So we can say that database design is so important.