Yeah but that's just a starting point, I know with me I select a standard daytime atmosphere to start with while I arrange the scene and do the texturing (so I can see what I'm doing more clearly) and then after I'm happy with that I load the atmosphere I really want to use and start tweaking from there. There's no rule you have to use the atmosphere you start with, the review seemed to imply that you HAD to set up the atmosphere you want in your final image first, that there was no other order you could go in, whether you select one or start with the default one (as most softwares do) you still don't have to start by tweaking the atmosphere.