When I think about my favorite photos, I must admit that they are a bit of both. Some were sheer luck -- fortunate grab shots -- while others were planned -- maybe not from a significant time beforehand, but planned nonetheless. For example, I might visit a site and realize a really good shot can be made by positioning my camera in such a way. Not really spur of the moment, but not exactly long term planning. Or I may see a developing situation and can predict a likely outcome which may be only seconds away, then I position myself for this outcome. Not quite spur of the moment.