What's "not to mention" mean and when's it used?

Native speaker’s answer
Rebecca
"Not to mention" is used to introduce an additional point or fact to reinforce what's already being said. It means that if what I already said wasn't enough, there's also this point. Ex: Watching that movie was a waste of time, and not to mention a waste of money too. Ex: I loved how awkward Harry Styles was at his movie premiere, not to mention the way Rolling Stones made fun of him on their social media.