A child theme is a theme that inherits the functionality and styling of another theme, called the parent theme. Child themes are the recommended way of modifying an existing theme. Layers is no different with the exact same principles applied to their themes.
Why Use A Child Theme?
The answer here is simple, when updating a site from one version to the next you never have to worry about breaking the theme or even any manual coding or custom edits your may have done as the child theme is active and the parent theme just sits in the theme folder. You just need to upload the new version of the parent theme and everything is updated.
I know it sounds way to easy, but that’s all there is to it.