Why to use stored procedure in database ?

1- Declare it once , use it many.

2- encapsulation , adding layer of security that can be placed on the database from the calling application.

3- the data functionality is separated from the application making it easier to manage, document, and maintain.

4- Improve performance .

I think it's reduce a performance and speed instead of writing a complicated query using code 

• Because scripts are in one location, updates and tracking of dependencies based on schema changes becomes easier and can be tested independent of the application.
• Having Stored Procedures in one location means that there’s no confusion of having business rules spread over potentially disparate code files in the application, and also stored procedures are cached on the server.
• Execution plans for the process are easily reviewable without having to run the application
•  Limit direct access to tables via defined roles in the database
• Provide an “interface” to the underlying data structure so that all implementation and even the data itself is shielded.