I was surprised to find that the Photos tab in Dropbox online (i.e. at Dropbox.com) contains bookoo pics from wayyyy back.
I've always deleted pics from the iPhone after naming and saving the ones I want to keep on my PC (in Dropbox folders of my own (conscious) creation). In Dropbox it says, "Camera uploads is turned off." Don't believe I've ever intentionally told Dropbox to save all photos.