CiviCRM Multiday Event creates multiple entity based events associated to a single Drupal node linked to a single CiviCRM Event. The duration of the CiviCRM Event last from the start date and time of the first session to the ending date and time of the last session. So if you have a class that meets every Friday in May, Drupal will display 4 events (5/4, 5/11, 5/18, and 5/25). CiviCRM will only have 1 event running from 5/4-5/25. This allows groups already leveraging CiviCRM for event registration, payment, reporting, and certifications, to continue using those components while making it easier to display individual events with Views.