Historically, migrating your content management system (CMS) or content platform from one major version of Drupal to the next was nothing short of a Herculean task.
Every new version of Drupal meant rebuilding existing functionality, converting (or migrating) your content, and accepting significant changes along the way. Because of this, it’s become commonplace to see stakeholders want to leapfrog Drupal versions (e.g., 5 to 7, or 6 to 8), to extend the life of both their old and new platforms for as long as possible for the least amount of transitional pain.