This question came up, and thanks to AlanOfTheBerg was brought to our attention.
These nodes are important and should not be deleted. They play a significant role in the routing algorithm. For cul-de-sac they are important - without them, waze will not be able to navigate you through the segment.
They are just as important to regular street.

Part of the process of building a route is when waze looks for the shortest way through 2 nodes. It then searches for the possible connections that will get you from node A to node B.
So when trying to navigate to a dead-end street, that has no node at the end, waze will basically refer to the node at the beginning of the segment (when the end one is missing). This is something we should try and AVOID, as some routing bugs could happen when the real end node is missing.

If you have deleted these nodes in the past, that's ok. We're currently checking for possible solutions for bringing these nodes back, and a way to make sure that they cannot be deleted as long as the segment exists.