It definitely has a lot of strengths - imagine walking around at night, trying to get shots handheld using only the ambient light. With a kit lens, unless you use a tripod or an external flash, you'd probably have lots of blurred shots or underexposed ones. With this rather fast lens, you can get crisp, clean and properly exposed images.
|Taken at the night market, Chiang Mai, Thailand (1/60sec, f2.5, 50mm, ISO 400)|
|Tuk-tuk and driver, Chiang Mai, Thailand (1/40sec, f3.2, 50mm, ISO 400)|
Another aspect of this lens (and other primes) that photographers obsess about would be bokeh. Take a look at the background of this woman's portrait and compare it with the one from the child's:
This picture was taken in daylight conditions using Niko and the kit lens, 18-105mm. Note that though the background is slightly blurred, it does not form the same shapes and level of blurring rendered in the above picture.
Another advantage of the nifty fifty is that on a DX body, this can already serve as a good portrait lens. Notice how people's faces (particularly noses) seem fatter when you use the wide end of the kit lens? This can render the person's face more proportionately, thus creating a more pleasing head shot.
The 50mm is also rather light, and you can barely feel the weight once mounted onto the camera. If you're not keen on carrying brick-heavy accessories in your photography bag but still want to get good shots, this is a lens to consider.
Despite its strengths, the 50mm lens also has its drawbacks. It is a nightmare (in my case) using this for group shots - my advice is to position the people you don't like at the sides so if anybody doesn't fit in the frame, it won't be your friends (kidding of course).
You need to do a lot of foot zooming to fill the frame with enough context in street shots, or group members. If you're used to just standing in one spot and turning the barrel of the lens to adjust the framed composition, this will definitely be a challenge for you. A lot of photographers also find this too long on the DX body for it to serve as a general purpose lens as well, often selling their copy and getting the 35mm f1.8 for DX instead (which is also a good lens!).
As they say, one man's trash is another one's treasure, and for those who like this lens, it's a very good companion for their camera body.