Distance to Subject
When flooding or "defocusing" your light, move it closer to the subject.
As you focus or defocused your light, you will want to move your light to an optimal distance from subject, to ensure you're taking advantage of the total the light output of your reflector. Below are some guidelines for this.
Since focused light is collimated (ie, travels in collinear or parallel rays), it will theoretically travel infinitely in the same direction without changing its spread. Think of focused light as a cylinder of uniform light rays traveling together. This means that no matter what distance the light is placed at, your subject will receive the same amount and coverage of light rays. In this case, moving the light closer or farther away from your subject will only change the the relative size of the light compared to the subject, and therefore will change the hardness of the shadows. However, this is only theoretical. In reality, any given lighting reflector in focused position will have some degree of spread, due to the reflector surface material, size/shape of the flash tube, tiny wrinkles in the fabric, micro variations in curvature, etc. As a general rule for focused light, placing the light at approximately 8 feet away from the subject is a good starting point, although the distance can be greater or smaller depending on your space requirements.
Flooded or "defocused" light has a wider spread, depending on the amount of defocusing. In this case, the light no longer travels in a cylindrical beam, but rather in a wider cone of light, that continues to widen as the distance increases. This means that, for any given lighting reflector at any given distance, some of the light rays will hit the subject, and some of the rays will spread out away from the subject. The same thing happens when using diffusion fabric, just that with a focusing system you can control with precision the amount of light spread. As a result of flooding the light, even though the total output of the reflector will remain constant, the intensity - and density - of light on the subject will decrease, since fewer light rays are hitting the target. This can lead to a very "dull" looking light, if the light is placed too far away from the subject. In this case, you will want to move the light closer to the subject, so that more of the rays from the reflector are actually hitting the subject. As a general rule, a Parabolix Reflector can be moved to approximately 2-4 feet away from subject when completely flooded. Since larger reflectors have more surface area, the distance can be greater for these.
Focused light in nature - Sunlight
Sunlight on a clear day is a great example of focused light. Light rays from the sun hit the earth in (nearly) perfect parallel rays, giving it the hard, specular look we all know. Because the sun is so far away from Earth (93 million miles), the light rays coming from the sun are collimated when they hit us, giving the light a hard "focused" look. Contrary to what some would say, the sun is not a true "point" light source - since it is about a million times larger than Earth - but rather behaves more like a "directional" light source, meaning a very large surface that emits light rays evenly all over (like a parabolic reflector). This is why a parabolic reflector gives a light quality similar to sunlight. A true point light source only exists in computer simulation software, since any real-world light source will always have a size, area and volume (for example, a xenon flash tube has a volume of gas that ignites and produces a small area of light according to the flash tube size).