This project is for use with a Composer-managed Drupal site. It is recommended that all Composer-managed Drupal sites use this project.
Require this project instead of the drupal/core
subtree split in order to guarentee that all of the dependencies from
drupal/core will be included in your Drupal site at exactly the same version
that was tested with the version of Drupal you are currently using.
The consequences of not using this project is that Drupal's dependencies may "float up" to more recent versions than were tested with Drupal when you use Composer to upgrade your Drupal site. Occasionally, new dependency versions introduce bugs in Drupal. While these sorts of errors are usually corrected fairly quickly, it can still be quite disruptive to be one of the first people encountering one of these bugs. Using the recommended dependencies avoids this problem by only using dependency versions that have already been tested with Drupal.
When using this project, upgrade your Drupal site as follows:
$ composer update drupal/core-recommended --with-dependencies
This will update
drupal/core and any needed dependencies.
Running a simple
composer update will also update
drupal/core, all of
Drupal's dependencies (to the correct tested versions), and all of your
contrib modules and other dependencies.