When they don't have any key in the environment configuration files.
In the UI, when a field is set in a configuration file, the field is
readonly, if not the field is editable. Which means you can selectively
choose which fields depend on the environment and which can use a
"default" value stored in database.
Automatically add <field_name>_env_default for every field transformed
to a "computed from env" field, so a default value can be set. It will
be used when the configuration is not set in a configuration file
(when the key is absent, not empty).
Guewen Baconnier