You are busy planning your post-apocalyptic game's visit to a shattered city, and no doubt your mind is full of the plot that will play out whilst the party is there... but to create the authentic feeling of an alternate reality, you'll want to add flavour and colour that doesn't have anything to do with the story... and that can be difficult to think up, especially when you are thinking about your plot.
That is where this product fits in. Just roll percentage dice and describe what's there. Local colour adding realism to the scene but quite irrelevant... or are they? Anything from an incidental encounter to a full-blown side adventure - or even something that contributes to your main plotline - can result, and you can of course hide the plot-related events amidst these others...
Maybe there's a young couple selling tie dyed clothing from a prop up booth on the city sidewalk (# 61) or three rastas armed with assault rifles stand guard at the front entrance of an apartment complex (# 91). Is there a story behind them? Do they know where to find whatever it is that the party is after? Or are they just what they appear? Only you know... but it all goes to add to the realism of the scene, making the shared alternate reality come alive for you and your players.