I talk about this all the time. In my opinion, having a quality of light is critical to producing a good image. Often times when we are shooting outside, and we are faced with direct sunlight and harsh shadows. Of course we always hope for slightly overcast days, but often times Mother Nature decides to challenge us with direct sunlight : )
To deal with shooting in direct sunlight, we always bring along our handy diffusion panels. On engagement sesslons we bring two panels, one small round panel, and a larger (larger is an understatement) square panel. By positioning these panels to essentially shade our subjects, we can achieve studio quality lighting in an otherwise harsh situation.
Here is an excellent example. In this shot we decided to selectivley diffuse the light hitting Mike and Lia. We liked the harsh contrasting lines in the background, and decided to use them as a compositional element in the photo.
This photo shows Steve using one of our small diffusion panels to "shade" Greg and Kristina.