Yeah, at least if a brake cable snaps you have the other brake. You'd have to be seriously unlucky to have both snap! And at least an electrical fault on your gears still leaves you able to ride in the gear you're stuck in.
A wireless brake failure is something I don't want to think about.
A few weeks ago a clubmate had a rear brake failure on a ride - it turned out to be cable slippage at the clamp so was probably fixable but he didn't realise until the following day. An hour or two later he hit a pothole hidden in a large puddle, came off the bike, punctured and buckled the front wheel. He had to release the front rim brake to allow the wheel to turn. So that is two brake 'failures' on one ride in the space of a couple of hours. Fortunately he was riding fixed gear so he could revert to full fixie hipster mode to complete the ride. This included the descent of a chevronned hill that I would definitely have walked down...