What is the significance of the overview slide in a presentation?

The first slide which follows the title page of my presentation is the overview slide. It has the title for each section to follow in the talk (thank you Latex!).

My question is how much time is to be spent on the Overview slide, given the talk lasts twenty minutes? Should I talk about each section's one-line-synopsis to let the audience mull it over? If the answer is no, how do I transition smoothly from the Paper Title Slide to the one on Motivation for the talk (For example : Why I love Science?).