A very important aspect of choosing which part of the subject shall be hit by which type of light source is something I consider very closely when doing a selective lighting exercise in my shoots.
As we all know, continuous lights and flash can have very different outcomes and knowing how to control those results is part of the challenge in adding dimension to your images.
I have been able to recreate to a certain degree the tilt shift look in an image without using a tilt shift lens, by just choosing which part of the subject will be sharp and which will be blurred. You can see an example of this in the shoot I did for Spoon Magazine in this VIDEO. You can watch what I am doing momentarily, attempting to have a subtle lower half blurred effect even when shooting perpendicular to the subject.
For example, to obtain this effect from the waist don, I will light the upper half of the body with flash and the lower half with either hot lights or kino light. I will shoot at around 1/4 to 1/15th of a second. As I am shooting the subject, I will focus on the eyes and just as I am pressing the shutter, I will do rapid pivot downwards to achieve this effect. Playing with the rapidity, will render different outcomes.
It has taken me years to perfect this and have had some success in doing so. Although not perfect, it is something that is difficult to replicate in Photoshop and can give you some very strong 3 dimensional effects. None the less, you can also see this technique employed in this VIDEO where I have flagged the flash and use Mandarine Tungsten light on the lower half of the models body.
Have fun and experiment. The sky is the limit.
What Kinds of Lighting Accessories are Needed to Sculpt or Paint with Light?