While in the air, or at a field location, or any of a hundred cafes, restaurants, even the occasional conference venue. Downed internet connections, and unavailable hotspot passwords are a real thing. I probably log a reliable 10 hours a months of offline work, though have had occasion to do much more than that at a single stretch.

As someone who isn't a web developer, the question seems ludicrous to me.

It's important to note that when you need to do offline development, you need to do offline development. A toolchain that requires an active internet connection is still fundamentally unreliable, even in 2015.