If everything had detail, it would become too literal and ruin the affect. When you see scenery in the distance, the eye isn't going to pick up on the details, but rather the grand image. I'm saying: I disagree with "DarkSteel" and think he was looking for an excuse to talk down to you. >_>
Not necessarily, but that is part of the process yeah. With this stuff if you want to get something down quickly there's nothing wrong with using a few textures here and there to get over an idea in less time.
You're right, it is about not relying on them too much but also using them in a way that speeds up the process. The only reason I only ever use them is for future practice, if I was to ever get a job in a studio I'd have to create something quickly, to a deadline. Obviously I'll have to create the composition, colour palette and idea myself first, but by using photos (sometimes) it just makes it a little bit easier to show things that aren't particularly important in the piece. If it was a fully painted piece with alot of time to create it I wouldn't use them as much