Drop And Again Create SP Will That Help???

Hi
I am wana to know why we every time drop the procedure and again create it as below...will that impact on performance or compilation of SP???

Use Northwind
GO
IF OBJECT_ID('dbo.ListCustomersByCity') IS NOT NULL
DROP PROC dbo.ListCustomersByCity
GO
CREATE PROCEDURE dbo.ListCustomersByCity @Country nvarchar(30)='%'
AS
SELECT City, COUNT(*) AS NumberOfCustomers
FROM Customers
WHERE Country LIKE @Country
GROUP BY City
GO

T.I.A