Incidence is great for when you have a lighting the same on your subject as the meter, close at hand. Formal portraiture is certainly one of these. Incidence is also helpful whenever you're shooting subjects that are hard to place middle tones (bride in white, broom in black tux-- but I wouldn't tend to use K64 for this!). Incidence is not nearly as useful at a distance. Spot metering is better, and it will also enable you to meter the brightness ratio/dynamic range of a scene, which is really the key to whether or not to load the camera with Kodachrome or print film in the first place. Kodachrome requires not only getting the exposure to within 1/3 to 1/2 a stop, but also calls for keeping the light within 5 stops dynamic range. So, meter AND bracket. Being most comfortable with it, I use spot metering most often-- in landscapes, wildlife, and environmental portraiture.