[ctdonath]

These estimates are completely useless in real life

Oh yes they are, for getting a grasp on what real life entails and what's possible.

With all the NSA scandal/hysteria going around, lots of people are approaching the issue with the presumption "gee, they can't possibly record everyone's phone calls". With a quick estimate I figured recording everyone, all the time, in CD quality, would take just 5% of the federal budget - making it doable instead of improbable or impossible, and making subsets of the scenario (i.e.: just recording phone calls) likely. For those of us who remember 10MB hard drives and 5.25" floppies, such a data scale is staggering - but it's a current reality, and a little estimating provides a reality check.

Likewise grasping the concept of, or even implementing, high-res "eye in the sky" drones. Gigapixel cameras seem like a novel futuristic impractical concept ... but then a little estimating involving HD-quality cell phone cameras, you can realize that a 24/7 flying 30fps gigapixel camera drone is in fact quite possible for a relatively modest sum (speaking in jurisdictional law enforcement budget terms). (Takes less than 200 cell phone cameras and a suitable multiplexer & high-bandwidth downlink BTW.)

I had an epiphany about accounting (!) when touring a billion-dollar timeshare (hotel/condo) project. Wanna make a billion dollars? Pick some large expensive project, then estimate your way down to a plan for pulling a few dollars out of a LOT of wallets by dividing, dividing, dividing away into manageable chunks people are willing to shell out a few bucks for.

Such estimates are exercises in how to mentally manage very large scale money, personnel, opportunities, and processes. Wanna make a billion dollars? Charge a buck profit per window to wash a thousand windows for each of a thousand businesses every week for 20 years. Don't laugh, there's some really rich people who made a lot of money charging a buck at a time - because they estimated their way into a profitable vision.

[peripitea]

In my experience, the rare quality is not the ability to do these estimates, but the ability to recognize situations where such estimates might be valuable. Most educated people can come up with reasonable estimates if posed the question, but far fewer realize when the question is worth posing.

Imagine a world where car2go does not exist yet. I would expect most of my friends to be able to roughly answer the question: "how many cars do you need to start car2go in City x?", but only a handful, if any, would have the imagination/insight to realize the potential and ask that question in the first place.