An outline slide in a lecture?
When giving a talk, no matter how good a storyteller you are, some significant percentage of your audience will be distracted at any given time. Outline slides are extremely valuable for helping those people catch up and rejoin your presentation.

What you don't have to do, however, is have a dry list outline. Whenever possible, I like to use a diagram instead, which unites the whole thing graphically, and indicate which aspects of the diagram we are currently dealing with. Nicely, this works quite well in chalk talks too.