The time you invest in designing a sound database structure is time well spent. Good design saves you time in the long run because you do not have to constantly revamp a quickly and poorly designed structure. You gain the following benefits when you apply good design techniques:
The database structure is easy to modify and maintain. Modifications you make to a field or table will not adversely affect other fields or tables in the database.
The data is easy to modify. Changes you make to the value of a given field in a table will not adversely affect the values of other fields within the table. Furthermore, a well-designed database keeps duplicate fields to an absolute minimum, so you typically modify a particular data value in one field only.
Information is easy to retrieve. You'll be able to create queries easily because the tables are well constructed and the relationships between them are properly established.
End-user applications are easy to develop and build. You can spend more time on programming and addressing the data manipulation tasks at hand, instead of working around the inevitable problems that arise when you work with a poorly designed database.