When students listen in lectures, often they are taking part in the discussion, thinking what they want to say, and often simply distracted by their environment for a few minutes. But I also don't want them so busy note-taking they don't engage with discussions.
Having pre-lecture handouts gives anxious learners an opportunity to prepare on the topic. Post-lecture handouts and assessments "fix" the information in memory. The secret to handouts, is to make it more than the bullet list from the slides or keywords they would have already noted down.
This video from the corporate training domain describes different types of learning materials, and when they can be used.