Shooting in dim lighting: While advanced mirrorless and DSLR cameras now feature impressive AF systems that can find focus in low light conditions, your camera and lens will often have to make a few attempts to lock onto a focal point - this is called hunting. Using manual focus removes this hunting, and allows you to make sure your image is sharp before you press the shutter button.
Fast and discreet shooting: As above, using autofocus can often be a little bit noisy, although this is a factor that has drastically improved in modern times. If you are photographing indoors, in hushed environments, or taking candid photographs in which you wish to remain unnoticed, such as in street photography, manual focus is the way to go.
People using manual focus in these settings often develop techniques to make the job quicker and easier, such as zone focusing - this involves setting your focus distance in advance and then selecting an Aperture that assures that everything within a certain distance range will be sharp.