Many zooms are so good you'd be hard-pressed to see much difference going to a prime at a matched focal length, unless you pixel peeped. Your main advantages would be speed and portability. But what if you missed getting an important shot because you'd left the zoom home? Can you try working with both? Whatever ends up on your camera most might be your answer. For one example in millions of people I shoot DX and my most-used focal lengths are 24, 50 and 105. I have a nice 18-105 zoom and that is on the camera most. But in low light or when packing especially light I take the 35/1.8. Its slightly better image quality and portability are nice. But once in a while I wish it were a little wider or a little longer. Styles of shooting will vary among people.