Amolitor's comments point out one of the biggest differences between FX and DX shots of social situations and closer-distance, urban/suburban environmental shots. DX shooters get the advantage of a little bit deeper depth of field at normal, everyday apertures, like f/5.6 and f/8. Using a DX Nikon to shoot walkabout photos, as well as social situations and family photos, snapshots, close-ups of interesting objects and plants and things like that...all of those types of shots benefit from at least one full f/stop's worth of deeper depth of field, and at LONGER distances, when shot using a DX sensor camera, the advantage might be a bit greater. Depth of field is easily quantified by on-line calculators, but the human brain's interpretation of out-of-focus, and the degree of out of focusness is much harder to describe. Numbers on their own do not provide the entire answer when it comes to depth of field, and what s considered out of fous,and what is considered to be acceptable enough to be noted and "seen". The main difference on smaller formats is that the depth of field reaches hyperfocal depth of field much more readily (SOONER, at shorter distances) with the smaller-sensor cameras than with an FX camera and lens combos.
See, depth of field is determined by several things, but one of the main influencers of depth of field is DISTANCE. With an FX Nikon and an 85mm lens, you can shoot a picture of a standing man and woman from 20 feet distant; with a DX Nikon, you need to move back to about 33 feet with the same 85mm lens. Now, the DISTANCE makes a big difference in depth of field. The smaller capture format also makes a difference. And because of the distance ranges involved here, 20 feet versus 33 feet, the way the background literally "looks" or "appears" or "is rendered" by the lens, is visually different.
This required distance issue, 20 feet versus 33 feet, means that an FX and a DX Nikon cause the photographer to use prime lenses, and zoom lenses, in very different ways. I'm not saying one is better or worse than the other, but there are very real differences, both in aesthetics, and in working procedures, in a good percentage of shooting situations. One of the huge advantages of using an even-smaller camera format like 4/3 sensor for "social photography" is the deep depth of field that the smaller sensor and its shorter lens lengths gives. The rise of high-quality 4/3 sensor cameras has enabled street shooters to get deeper DOF, and smaller lenses, and to be able to literally "pull deeper depth of field" to make pictures that, for example, would NOT be possible to make using something like a 120 rollfilm camera.