Bootstrapping with defaults included in the configuration / jar-dependencies, is the real advantage of Spring boot! Get the things done quickly!
Its just another project from Spring framework, where things look simplified, with strong support for Security, Data, Social etc all features you want for your application.
If you prefer annotations over XML configuration like me you might use
@Configuration for configuration,
@ComponentScan for Dependency Injection,
and @EnableAutoConfiguration to tell spring to guess the defaults
and work along.
The @SpringBootApplication annotation is equivalent to using
@Configuration,
@EnableAutoConfiguration,
and @ComponentScan
with their default attributes.
So things further simplified, with a single annotation doing the work of 3.
