What is the significance of the overview slide in a presentation?
I often skip the overview slide in short talks. Instead, after giving motivation I simply say what the talk it is about: This talk will introduce you to Nutella, analyze its deliciousness, and compare it to peanut butter. Finally, we will talk about Nutella extensions - chunky Nutella, with chopped hazelnut.

In general, the overview slide allows the listeners to pace themselves, and understand where in the presentation you are.