if you want depth to an image, you will only get that with a long lens. Notice that most 50, 75, 100, 120 mm fixed (prime) lenses are referred to as portrait lenses? The focal depth adds a great effect to any photo just so long as the subject fits in the view finder. I have been known to stand about 80' away from a subject just so i can use my 70-200mm L lens @ 200mm.
The other thing you may notice, is that prime lenses are faster - depending on which models you're looking at. I have a 50mm F/1.4 and a 75 F/1.8. Not that you will shoot that wide much, but when you do a low light shot with long exposure the effect can be quite impressive.
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