Complete Split

Some configuration, such as the fact that development modules (Devel, Kint, Stage File Proxy, Views UI, etc.) are enabled, should only apply to certain environments.

But configuration management in Drupal works best by always exporting and importing the whole set of configuration for deployment. To avoid deploying configuration for development modules one would have to manually remove the configuration from the sync directory before deploying and adding it again before importing changes from other developers. It is not possible to use the Configuration override system to enable or disable modules.

This is what the core of Config Split does automatically.

You define which modules you want to split off and all their configuration will be removed from the sync directory and saved in the split directory when exporting all the configuration. You can also add other configuration to be split off and exported to the split directory.

The splitting while exporting and the merging of the split directory only happens when the split configuration is active.