Each content type in Drupal comes with a body field. You can choose not to include the body field in your custom content type. Note that throughout Drupal, the body field is used as the default field when showing or emailing content. For example, when creating teasers on the homepage and for taxonomy terms, the body field is used. When sending notifications, the body field is used. Remove the body field or use it for data that might not always get filled in and you might have blank default teasers and emails.