Is the "checkout scm" step necessary in multi-branch pipelines?

[Behrang]

In my pipeline I don't have this step and everything is working fine, but most articles I see on the web have this step in their Jenkinsfile, for example this one from the official Jenkins web site: https://jenkins.io/blog/2015/12/03/pipeline-as-code-with-multibranch-workflows-in-jenkins/

[Steven Foster]

I think it's a feature of declarative syntax rather than multibranch. In declarative, every time a node is allocated it comes with a checkout scm by default.