One of the skills a photographer is supposed to have which I have not yet (and perhaps never will) is pre-visualization. This was one of the shibboleths of the Adams-Weston crowd, and the basic idea is that you’re supposed to know what’s going to come out of your camera before you go anywhere near the shutter.
This approach is doubtless not just a virtue but a necessity when shooting film with a large-format camera in Yosemite; one can hardly afford to waste time and material, and it’s not as though you could check the LCD to see if you got it right.
None of those conditions apply to me, so there is no necessity; I am not sure whether there is virtue. Almost all my pictures are of targets of opportunity, and I generally have no more than one to five minutes to get out my camera, take as many shots as I think may get me a useful result, and then pack up and move on.
This ubiquitous capture approach has several virtues — it cuts down on the number of things I _wished_ I had gotten a shot of; it encourages me to pay attention to the world around me all the time, not only when I’m in a place where I should expect to find pictures; and most of all, it lets me catch things — like the two or three good shots of black-crowned night herons I’ve managed to snag — that I would otherwise stand little to no chance of getting, unless I set out to get them and then proceeded to make it almost a full-time job.

But it’s also the case that the pace influences the process, not just the output; I hardly ever try to get good composition in-frame; I usually place the subject (or at least the point of focus) dead center and compose after the fact by cropping.
More drastically, I often find that the main subject of an image is not that one I seem to have thought it was when I took the picture; for example:

There is a clear main subject, and it’s obviously the most interesting thing in the frame. But this is the original file:

I only noticed the interesting bit at the stage of cropping and post-processing.
I don’t think of photography as a creative art (I don’t generally stage pictures or engineer situations for taking them), but more as an analytic craft, like non-fiction writing; it is more a matter of peeling away what does not belong than of putting in what does. Given this, it doesn’t seem to me that it makes a difference to the product at what stage in the process the peeling occurs. What is more, I think it means I can apply to photography the rule I apply to writing — if I finish with precisely what I set out to produce, I have missed an opportunity to learn something.
Which, I suppose, means that I don’t take my inability to previsualize as an absent virtue, after all. Bitchin’.