[tcmb]

Maybe not what OP had in mind, but there's also the issue of taking hidden photos of others. If you're holding your phone in my direction, I don't see what's on the screen, but an LED on the back could let me know that your camera is on.

[jrockway]

Given that everyone uses cases, I doubt the LED would be visible.

People are always filming you in public, in the hopes of being the next viral Instagram sensation.