Many of us take photos on the streets and in most cases we don’t run into any trouble doing it. However in some cases even serious it can result in serious injuries if you take photos of people without their consent. Even if the law doesn’t require permission it never hurts to have it.
A British street photographer got beaten and his camera broken because of taking a photo of a couple on a street festival. Laws are on his side, but it meant not much against aggression.