It is most helpful here if students are the ones who verbalize what was learned. It is also appropriate here to move students toward possible applications for what was learned. If the lesson development did not go as planned, then closure may merely be a temporary stopping point, with less elaboration, until you can resume tomorrow. Learning theorists tell us that it helps us to retain new knowledge if we can link it to what is already known and can chunk it in related pieces. This is the purpose that closure serves.
Closure is important to retention of information and concepts.
It is important, then, to watch the timing of the lesson so that ample time will be reserved for the closure. Remember, you will always have tomorrow. What you try to stuff into children's heads in the fleeting moments of a lesson probably won't be retained anyway. The time would be better spent in a good closure, saving other new information for another lesson. You should be evaluating all along.