Enabling multiple submissions also shows that you trust your students, allowing them to see their feedback immediately and take corrective action. This also alleviates some of the anxiety students may have around the use of Turnitin by using it in a non-threatening and supportive way.
This strategy is great at the beginning of a course when students are still adjusting to the new coursework and instructor, and as a way to reinforce the importance of proper source integration. As stakes increase later in the term, you can start to raise expectations as well and not allow the multiple submissions, though formal draft assignments are still recommended.
Learn more about this classroom strategy and more by joining the on-demand Turnitin Academy class, Best Practices for Teaching with Turnitin »