If you see something local you want to photograph, do it - now. Even if the conditions are not 100% perfect, do it. You can always return and try again, but at least you'll have something, which might end up being the right shot anyway. I keep getting taught this lesson the hard way, but I never completely learn it. I've been stalking an industrial location for months. I drive past it every day on my way to work. There was always something not quite right. Wrong sky, too much wind, etc, etc. Today seemed like it would finally be the right day. Unfortunately as luck would have it, idiots chose last night to tag the place. Now it's totally ruined. No photograph. Gone forever. I'd also like to add people caught doing that, or found to have done that, should be forced to clean it with a toothbrush, then be stripped naked, covered in spray paint and marched throughout the city for people to throw things at.