Street portraits differ from street photography; in one you are capturing a "decisive moment" and in the other you stop the moment, take charge and get the shot you want. As a portrait photographer I like to take control; I want the light a certain way, the pose a certain way, the look a certain way. To keep things natural and realistic, I will often leave things pretty much as they are, especially with street portraits, but I always like the light to be nice. Whether using natural light only or adding a reflector or fill flash, the light has to be nice.