If you come from the JavaEE world you probably did set some of your project dependencies to the scope of provided if so then you can find one fact about spring-boot-maven-plugin to be interesting.

After adding provided scope to a dependency you expect that JDK or container (like JavaEE application server) will provide this dependency at runtime. Expected behaviour when running application without providing these dependencies will be to see NoClassDefFoundError or ClassNotFoundException all depends on how these missing classes are accessed (for more information see this article). But this is not a case when using spring-boot-maven-plugin to run your application in standalone mode i.e. outside of any kind of container. After reading the explanation from Phil Webb (Pivotal) this behaviour makes sense:

The packaging of provided scoped jars is intentional. The reason for this is that many developers are used to adding things like servlet-api as provided. Since there won’t be a servlet container to actually “provide” the dependency we package it inside the JAR.

Source: https://github.com/spring-projects/spring-boot/issues/413#issuecomment-36361340

In spring-boot-maven-plugin sources we can find how dependencies are loaded for run goal.

AbstractRunMojo.java:

private void addDependencies(List<URL> urls) throws MalformedURLException, MojoExecutionException {
    FilterArtifacts filters = (this.useTestClasspath ? getFilters() : getFilters(new TestArtifactFilter()));
    Set<Artifact> artifacts = filterDependencies(this.project.getArtifacts(), filters);
    for (Artifact artifact : artifacts) {
        if (artifact.getFile() != null) {
            urls.add(artifact.getFile().toURI().toURL());
        }
    }
}

this.project.getArtifacts() loads all project dependencies including transitive ones (provided scoped are loaded as well!). After, the load is done we removed dependencies based on configured filters - by default only test classes are removed. Yet it is still possible to make some exclusion in the plugin configuration.

Conclusion

When your project deliverable is a war file that will be run in a container then it is very pleasant to be able to run it in standalone mode without additional tweaks when there are some provided scoped dependencies.