They are simply ci/cd templates for building specific types of projects. If you turn autodevops on, then it will apply the template based on files found in the repo. Like a less opinionated Heroku that can deploy to your own k8s cluster.

I have never really had a project generic enough that autodevops would work. But I think I did at one point copy one of their templates as a basis for my own gitlab-ci.yaml file.

I think it also handles automatically configuring some things that you can't configure in your ci files, like prometheus monitoring.