Smoke and Mirrors?

I've seen a few scooter sites that show their scooter on the beach, at a grassy park, airborne doing stunts... but what bothers me is these are stock scooter photos superimposed onto other images to make them seem life-like. Why do people do this? Is this a good idea - faking images?

I bring this question up because of this recent photo set:

Iran lost launch capabilities of one of its missiles in this week's test. In order to keep their enemies from thinking they messed up, someone over there edited the original picture before making it public to try and make it look like all 4 missiles launched. Is this a good idea - faking missile launches?