Completion of my fractal for me is when I've reached something pleasing. That's not to say I don't take it further or morph it a bit, I do. Sometimes I end up with a "series" of fractals I like equally well that are all spawned from the first one I liked. On the other hand, I can sometimes play away for days and not come up with anything that pleases me and all those bits of chaos are gone forever. This state would mirror my painting tangents where I just mix colour up for the sake of being able to touch it and psychologically fall into it. This process sometimes feels just as good as creating an image :)