Fabien Potencier of the Symfony project has a post on his site that introduces Symfony Packs, groupings of useful packages that can enhance the functionality of your application without having to manually load each package individually.

We get a lot of positive feedback on Symfony 4. You love the new directory structure. You love the simplicity of using services without configuring anything. And you love the automation that Flex provides. It makes me happy and proud.

[...] But one issue I hear sometimes is that it is more complex to start a new project. [...] You loved the simplicity of starting a project with the Symfony Standard Edition. Is it nostalgia? Perhaps. Would it be possible to get the best of both world? Certainly!

The Packs are "metapackages" that Composer uses to bundle dependencies together that relate either in functionality or as defined by a custom configuration. The article gives an example using the symfony/orm-pack pack and talks about how you can use it as-is or you can "unpack" it into its separate packages and automatically update the composer.json with the result.