[mfonda]

Being able to approximately estimate numbers is an excellent skill for software developers to have. Imagine you're running some operation that affects N things or has N results. After seeing the results, it's very helpful to ask yourself "Does N roughly match what my intuition/estimate told me it would be?" If your estimate is off by at least an order of magnitude, it's a hint there could be a bug in your solution and that it warrants a closer look.

I don't ask brainteaser type questions, but I can see their appeal given the value of estimates. I also don't see why they're so universally hated. Is doing back-of-the-napkin math something a lot of people struggle with?