civicrm_subscribe is a Drupal 6 module
This version is a straightfoward conversion of https://www.drupal.org/project/civicrm_subscribe module to CiviCRM api v3 that is required from CiviCRM 4.4+
As mentionned on civicrm_subscribe page :
For most cases, colemanw's CiviCRM Webform Integration module should be a better and more extensible choice. The only reason you would want to use this module is if you didn't want to use the Webform module and just wanted to submit an email address.
I only suggest this for those who have Drupal 6 with civicrm_subscribe already installed and want to update to CiviCRM 4.4 or more before switching to Drupal 7/8.