Question about MySQL Host & wp-config.php

Hi there.

Just a quick question regards a database that I am migrating from an old shared hosting setup, to a new shiny London-based VPS.

These are the 4 definitions within the wp-config.php file which connect the database.

/** The name of the database for WordPress */
define('DB_NAME', 'eg');

/** MySQL database username */
define('DB_USER', 'eg');

/** MySQL database password */
define('DB_PASSWORD', 'eg');

/** MySQL hostname */
define('DB_HOST', 'localhost');

My question, when connecting to a newly imported database (imported via PHPMyAdmin) should the DB_Host be localhost, or the IP address of the Droplet? What are the differences?

Thanks a lot.