Skimboarding I, photograph
“Exaggerate the essential; leave the obvious vague.”
– Vincent van Gogh
Every image has obvious elements – too often we find ourselves representing these qualities in excruciating detail. Why? Well, it’s… obvious. It’s easy and comfortable. It can make the viewer comfortable, too, and anticipation of that can compel us as well.
What is essential, on the other hand, requires some thought. We have to abstract from the obvious, sometimes deconstructing it, to reach what is essential in the scene. We may get it wrong, or we may not be able to express our conclusion well. It’s riskier than the obvious, but it is only when we stretch to touch the essential that we have any opportunity to make a real connection with the viewer. I think what draws people to art is the chance to connect with the essential and skip past the obvious that surrounds our daily lives to completely.
Part of my fascination with images partly out of focus is that it allows me to be intentionally vague about elements in the image that are not essential. Vagueness can be an enigmatic quality, a tool to employ to help with the essential. Just as the eye is attracted to the area of greatest value contrast in an image, the mind is drawn to point where the vague and obvious surrounds the exaggerated essential.
Bob Cornelis' Art Blog 
And because this runner is vague, he becomes Every Runner in a way. The viewer can see themselves or someone they know in this image, should they decide to do so.
You had mentioned in a comment on Donna’s blog Layers about the lack of tactile texture in photography. It’s an interesting observation. But I still think photography as an art medium is nonetheless sensual.
I think your are right– vague, blurry, out of focus invites and engages the imagination more– more intriguing than showing every detail. Have you checked out John at Typos.Daily.Fate?
his blog is: http://starsandprayers.blogspot.com
Another thing that vague does is reveal subtlety, and show that the world is actually energy and motion, not just the concrete reality we assume it to be. You commented (more than once) on the “body parts” in my paintings, which I think is the same thing as your vagueness.