The prologue discussion was how prologues were often superfluous to the story.
But they talked a great deal about how important it was to give your character backstories. And how in the hard-boiled fiction, for instance, it is implicit in the detectives' actions that they served during the war -- World War I at the time. (The war tends to drift later) It's their reactions to dead bodies, which shouts of seeing trench warfare. Or would have at the time.
the importance of a character's backstory in influencing his reactions, like why he reacted so violently to things. (Indeed, they overdid it. Your backstory doesn't determine your character as much as they seem to think, because you could build an entirely different and completely plausbile character from the same events.)
One panelist mentioned he had a happy childhood, and as a consequence, had to be to put in that his characters' family was loving, he had just assumed it.