Coupling refers to the degree of direct knowledge that one class has of another. The less your components are tied to each other, the better. Using a DI framework has many benefits -
Dependencies are handled through the provider framework making your application code more flexible, reusable and scalable.
Using a DI Framework to manage the singletons in your applications. Singletons without a DI framework may hamper your testing.
Encourages the Program to interfaces approach.
Makes for an excellent architectural glue providing consistencies in how you would configure
JDBC, JMS, Javamail, JNDI and any other API's.