Vertical "Letter Box" Videos
 

Why on earth do we see so many video recordings, always shot by amateurs, presented in this bizarre clipped format with the outside thirds blurred out and only the middle third visible as a weird and almost unwatchable vertical strip even when there is clearly useful content behind the outer panels?

See the pax video of the recent Dash gear collapse at EHAM for a particularly idiotic example.

Filmed from mobiles.

Filmed vertically on mobiles by people who don't know that videos are best shot landscape. The blurry side bits are not useful as they are just a blurry repeat of the main video. Would be better left black, really.

More than likely its one of the effects available to snapchat users

Agree, the useful content you mention is not there, it has been added by editors to avoid a screen that is half black. Have a look next time and you'll see it's just a repeat.