When you select a supplier or a customer for an account invoice, you see the contacts of the companies. With this module installed, you will see only the main companies or the contacts who do not work for a parent company, which makes more sense and makes the dropdown get rid of useless options.
This module is maintained by Anubia Soluciones en la Nube, S.L.
For more information and questions, please visit: http://anubia.es/en.