Wanting to reduce the number of lenses I owned prompted me to consider one zoom that covered the focal length range of a couple of lenses. By gettng an 18-70mm, I could get rid of my old 35-70mm and the 18-55 VR kit lens. So I bought a used Nikkor 18-70mm 3.5/4.5 G ED. The only thing I would give up was the VR.
I didn't want to wait to get home to do test comparisons so as soon as I received the 18-70, I went and borrowed my co-worker's 18-200 and made test shots at 18mm, 55mm and 70mm. I was completely baffled by the results. I thought they would pretty much be the same. It appeared that the 18-70 had a wider angle of view at the same focal length as the 18-200.