The harshness of the light is also important because it dictates the contrast level in a scene - the difference in brightness between between the highlights and the shadows. In sunny weather contrast is high because you have bright highlights and deep shadows mixed together, whereas on a dull, overcast day the brightness range is far smaller so contrast in lower.
Colour film can record a brightness range of about seven stops, but if you shoot around midday in bright sunlight, or include a light source such as the sun, that range will be more than the film can handle. If you expose for the highlights the shadows will block-up, but it you expose for the shadows the highlights will burn-out.
Your only options is to decide which part of the scene is most important - the highlights or the shadows - and expose for them. Or, you could compromise by taking a meter reading from both and finding the average.
With subjects like portraiture and still-life you can control contrast by using reflectors to bounce the light around. This isn't possible with landscapes and architecture, so you either have to make the best of what you have or return when the light isn't so contrasty.