Segments are useful to create a dynamically updating pools of your customers. For example, to have a list of users from a specific country, visited your website X times and, have last seen date more than 30 days ago, simply go to the 'Contacts' section, use advanced search criteria and hit save button.

Once created, segments can save your time while creating auto and manual messages. They can be loaded right the way, without choosing same rules over and over.