It is fast.
With a maximum aperture of f1.8, this lens is between 2 and 3 stops better than a zoom lens at the same focal length. When I say "fast", I mean it lets in more light, so I can shoot in low light conditions without using flash or use a faster shutter speed thus reducing camera shake. The wider aperture also means I can also reduce the Depth of Field more if I wish.
It is sharp.
Prime lenses have no moving lens elements within them, unlike zoom lenses. They also have fewer glass elements within them. That means less internal refraction of light resulting in a sharper image than a zoom lens at equivalent focal length.
Here are some images and a cropped sample for each image. (All images at f1.8)
It is light.
A short focal length lens like this weighs next to nothing. I can carry it around in my pocket all day and never feel weighed down.
It is cheap.
Unless you are in the market for a really fast Pro lens, prime lenses are relatively cheap, especially in the used market and there are plenty of them around.
It assists creativity.
??? While at first appearing restrictive, using a single fixed focal length forces the photographer to actually more around a lot more to get a good composition. This forces a change in viewpoint and stops you being lazy in your approach to creating a photograph.
The 35mm is the "standard" lens.
The 50mm prime lens is considered to be the "standard" lens for photography as it's angle of view is most similar to that of the human eye at rest. However the 50mm lens is only "standard" in terms of old 35mm film cameras (or DSLR FX lenses which have a 35mm sensor). My camera like many consumer DSLRs has a "cropped" sensor which means that any lens focal length should be multiplied by 1.5 to obtain a 35mm equivalent. Thus my 35mm equates to a 52.5mm lens on a 35mm or FX camera. Near enough the "standard" lens.
This means it is a good lens for street photography or landscape photography.
So, don't write off prime lenses. They have their place even in this world of super-zooms !