I've found making photoscenery very easy.
But other than for scenery development, I'm not seeing any use for a purely flat texture (with mesh elevations).
With autogen, however...
Installing the photo scenery does seem to cause autogen objects to go away. However, that is not always bad; I noticed with the MegaCITY USA 2005 - Dallas/Fort Worth scenery that autogen buildings were being placed on top of roads, and other such silliness.
It doesn't remove buildings built into the scenery, or airport objects; here are some shots of Las Vegas with photo scenery showing both:


Photo scenery looks best from 3,000 to 5,000 ft anyway. I think it is better to intelligently place some landmarks in the right locations than to let autogen place objects in the wrong places. (If you don't know a city very well; autogen does a respectable job; but photo scenery is nice if you know a city well, and want to see all of the streets, buildings, railways and other landmarks in their correct locations.)
-James