Civicrm is an open source 'Customer Relationship Management' system. It is mainly targeted at membership organisations and NGO's which are also a major client base of MountainRiver.net. Most of our site templates come with it pre-installed as we find it solves some very common problems. CiviCRM and Web Form are the most common 'value adds' that MountainRiver.net provides.
Emailing groups of customers is still a highly effective way of getting in contact with people. Sometimes people need some prompting to return to your website and if the content is relevant and carefully produced a mailing can be valued by your customers.
CiviCRM provides this service very will with bounce tracking (critical), deduplication (also critical if you don't want to be listed as a spammer) and opt-out (legally required). CiviCRM provides friendly editing interfaces and integration points.
CiviCRM also reduces the need for expensive 3rd party services such as MailChimp and reduces the integration effort required to effectively use these systems.
CiviCRM is also useful as the backend of a shop system. Customers can be added to CiviCRM so that shop owners can maintain contact.
Loyalty or Subscription services can be built on top of CiviCRM solving a number of ecommerce needs.
In short we install CiviCRM for you, as even if it is only used for mailing this is an extremely useful service.