Manual focus, zone focusing, and hyper-focal distance

Manual focus might seem like a daunting prospect, but it is not as difficult as it sounds and it can really open up many possibilities when it comes to street photography. The main advantage of manual focusing over auto-focus is speed. Yes, it can be faster to manually focus rather than letting the camera seek focus automatically, regardless of whether you're shooting with a high grade camera body or not (sports photography, certain wildlife photography, etc. are exceptions due to the erratic motion of the subjects). This is especially true in good light because it allows shooting at f/8 or f/11. At small apertures the depth of field, or DOF, becomes large. Also, with sharp lenses, one does not need to nail focus exactly on the subject. Even if focus is slightly off, the subject will be sharp due to the large DOF. When using auto-focus, the camera will search for perfect sharpness which increased the time required to focus.

With practice, one can very quickly guess the approximate best focus with great speed and accuracy. In addition, depending on the auto-focus settings (matrix, spot, etc.) the camera might not focus on the desired point in the frame. The photographer has more control over what should be in focus, and most importantly can make the decision more quickly with manual focus. There's no need to mess around with focus select points and little joysticks on the back of the camera body. Selecting the focus point happens instantly in your mind.

But this isn't the real advantage of using manual focus. Modern AF systems have come a long way, and can nail focus on eyes and faces even in extreme conditions. The real advantage comes with having the focus already setting before you even know what your subject is. Then there is no need to focus at all.