All artists have the issue of when to consider their work 'done' and leave well enough alone. Painters, composers, architects, writers, they all have to deal with it. And some, like sculptors, only get one chance to go too far. You can't add marble back very easily. In some ways, photographers have it better than most because by nature our art is much more structured if you want it to be. Press the shutter and be done with it, creating the negative is their final creative decision, the Cartier-Bresson way. Then again he was a prissy, french, rich boy.
Further down the scale are those people that used to mess in the dark room. It being an analog process, every print is different so there are a lot of decisions to be made in that process. Chemical and paper choices, dodging and burning, print size, etc. Now of course, most of us play in the virtual darkroom of PhotoShop. Anyone whose seen my work knows that I'm not immune. I'll often spend 2 hours or more on an image. Playing with curves and color correction, saving and walking away. Only to come back and tweak half the stuff I did. Refine it in an iterative process.
For me, I work on getting it the way I want and then at a certain point I switch and start looking for flaws in my work to fix by cleaning up sloppily drawn masks or tweaking curves to blend better. The point at which I'm happy is when my pictures look like my work, but at the same time look like they couldn't be any other way. I know it's ethereal and gray, but it's the best I can put into words. My workflow has been this way for a while now, but my standards have certainly gotten more strict. The cleaning up stage has gotten longer and more anal. I recently entered a competition and in the process of choosing and prepping my images, I spent hours refining post-production that I had considered "done" back when I shot them. The older they were, the more work they needed to look finished in my mind. And we're talking 8 months for the oldest, not 2-3 years.
So, the question is, how do you know when you're done? When to back away and say, "I'm finished, this is the final product"? I realize that this is a subjective question; I am looking for opinions. Also, is it ok and/or right to go back and refine them? Should you leave well enough alone? Did Picasso go back and add paint to a 10 year old canvas? And if you do go back, do you make a copy of the original and consider the new one a different version? Interesting stuff.