I go to a lot of meetings. Great facts, ideas, and instruction are routinely provided. I’m always amazed at how much is missed by the audience.
Discussing with the presenter seldom adds much, and cuts down the time for presentation for everyone else. As a related model, when I read a blog, if I have something to add that supports the premise, I comment. If I want to disagree, I go somewhere else, maybe write a positive blog about my point.
Here’s a model for getting the most out of a face-to-face presentation.
Get there early.
Later, transcribe your notes, adding what should have been. Define your action list.
Check your work with others attending. Improve your notes based on feedback.