Lets look into the benefits of a Prime lens and for the interest of this post, the 50mm prime specifically.
1. 50mm Primes are among the cheapest prime lenses to purchase. Even some of the top of the line designs are cheaper compared to other focal lengths. This is where the term "Nifty Fifty" came from.
2. Primes allow you to achieve a narrow DOF ( Depth of Field ) which will enhance subject isolation and bring the viewers eye towards whats important in your photograph.
3. Wider F-stops like f/1.4 through f/2 allow for two advantages in addition to subject isolation. You will achieve faster shutter speeds to ensure crisp sharp images in failing light as well as lower ISO numbers which offer better noise control.
4. They are usually lighter and smaller which offer obvious benefits.
5. A 50mm focal length or focal lengths within that range offer a great combination of compression for portraits yet wide enough to go walking about and tell your story. If you look at the image above of my daughter holding onto the telescope viewer at Niagara Falls you can see the surrounding elements that are important in telling this story. You can see the binoculars, you can see the mist from the falls. The buildings and people around her. You can even see her clothing which tell you it was a nice sunny day. Had this shot been taken with an 85mm or even a higher telephoto focal length these important factors would of been left out of the image. It would be a tight portrait of a child and thats all.
6. BOKEH !!!! We all love it even if some of us have no idea what it is. We know it when we see it. Bokeh can be explained in THIS article.