I'm running the tech for an educators' meeting this morning (I wasn't involved in the preparation of this presentation). As is customary, the presenter provided their PowerPoint slides as handouts to the attendees. These were printed the day before, but the presenter mentioned to me that she had made some quick changes last night. A few minutes in, she advanced to a slide that wasn't in the handout. I underestimated the repercussions – nearly every attendee began flipping through the handout searching for the elusive missing slide! Their attention was completely diverted from the presenter – who either didn't notice or didn't think to explain that the slide was missing from their handouts.
To add to the disruption, I was controlling a pre-loaded version of the presentation for a webcast. I also received the slides before the edits, and was not sure whether I skipped a slide, missed a slide, or what!
This is just another example of the drawbacks to providing handouts to the audience before the presentation. It is better to prepare a proper document to accompany the presentation (not just a copy of the slides) and provide it after the presentation.