[baq]

Vertical video is perfectly fine if the device on which it is played back on has a vertical screen. Never is very out of place here.

[immibis]

And that's the vast majority of devices that are used to watch videos. "Vertical video is never fine" stems from the good old days of PCs with monitors. In these phone days, according to the same logic, horizontal video is never fine.

[ryankrage77]

But the phone can easily be rotated to landscape, so landscape has wider compatability.

[shadowgovt]

For something you want to capture immediately, the amount of time it takes for the phone's accelerometer to decide you have rotated it is already too long.

[falcolas]

If, and only if, the application supports it. Frustratingly, not all do, so you're stuck with the biggest black bars framing a microscopic landscape video.

Contrast with a monitor, where it will at least be viewable vertically, even if it too only fills a portion of the monitor horizontally.