It's mostly my trying to understand my hero's motivation and disposition. As you play through the game you participate in events that took place in the past, so you're moving through time as you level up.
But I'm trying to pin down things like, at max level, from my character's perspective, how long has Statesman been dead? Was that weeks ago and it's still fresh? Or has Paragon city been without it's nominal Paragon for years now? The Mot Crisis was, as we see in this thread, in March of 2012. Are people's bruises still fresh, or have the nightmares had time to fade?
I'm just the sort of dork that wants his headcannon to fit within the official framework.