They shine a light on change, let us compare our world with that of four years ago, let us notice all the tiny things that have happened, all the opportunities and innovations we've introduced.
So, I'm going to spend a couple of weeks looking at the big themes from these Games, and I'm going to start with "openness".
On the face of it, that's an odd theme for an event that has been surrounded by controversy, rumours and leaks, but that's possibly because we've become used to an elevated level of "publicness" that we've stopped noticing is there. But think about the access we get these days, the glimpses we get behind the scenes - not just in the post-hoc documentaries but live, as it's happening. That's genuinely new.
Most obviously, there are the Tweets from the athletes, giving you a feeling of direct connection and, while it's never entirely unfiltered sentiment - today's athletes are too professional for that - you get a sense that you're getting closer to something authentic. And you certainly get to see inside in a way no old-world broadcaster would have bothered to show you. The mundane stuff of practice and training, of chat and living conditions - the things that give you a real sense of athletic life: sports stars as people.
You also get an authentic whiff of the mundane on the BBC's 24 channels of cameras pointing at every bit of sport they can find. Tuning into something without commentary, or to a camera pointing at a room full of empty table tennis tables, gives you a sense of unobstructed viewing, like you'd snuck in unofficially - not the usual groomed, manicured, montaged-to-death stuff of sports coverage.
But I'll confess my favourite bit of openness is slightly geeky - it's the way some of the tech and media people are telling us what they're up to in covering this massive event. So, for instance, @rogermosey is the Twitter account of the BBC's director of London 2012 and he has actively engaged with his audience, explaining editorial decisions, pointing out where people can find coverage and having little pokes at International Olympic Committee timing failures. Similarly, @alexbalfour2012 is LOCOG's head of digital and he does regular updates about its traffic, its app downloads and pointing out things such as the fact that London 2012 gets more traffic from mobiles than desktops. This is useful stuff for the UK digital industry - it raises the bar for us all. The Games are an opportunity to learn about how big audiences really use digital media tools and it's fantastic that people are sharing what they're finding.