Super Duper Fixie brake. This is {was} awesome lol {Repost sry}

but a caliper doesn't have the stopping power of a disc. like the guy says, it's nice to be able to lock up the rear wheel with one finger (providing the chain doesn't snap).

You can lock up your wheel (rear or front) with a caliper quite easily.

A disc brake (with sintered pads) would have an advantage in the wet - but would you want to lock your wheels up in the wet ?