Prime lenses are terrible . . . IF you don't know what you are going to be shooting. If you have a reasonable idea of what is going to be in front of your camera, a fast prime lens is better to a degree many people would never notice.
Click any picture to see it larger/at higher resolution. Especially click on the crops because these 400 pixels wide thumbnails Blogger requires do NOT do these pictures justice.
Here we have a shot from a couple of days ago with my general purpose zoom lens. This lens is decently sharp for snapshots but none too fast. I had to focus manually because of the foliage confusing the autofocus robot, and manual focus is an afterthought on this lens. It's not all that smooth-turning and the stop-to-stop focus ring movement is pretty short. Still, for a snapshot it is okay. This was as wide as the aperture gets, f/4.5 at 70mm, ISO 400 1/160 second exposure.
Say hello to Mrs. Cardinal:
Here she is at just over 100% magnification. You can tell what you are looking at, but the sharpness is not what I want. You can see she is in focus because there is some stuff behind her head also in focus, as well as some of the nesting material in front of her. It's focused, but the sharpness . . . well . . . .
Here she is a few days later. This is through a 100mm f/2.8 prime lens wide open. It's at maximum aperture so the contrast is a little low. The photo from the other day was around 14:00 and bright sunshine. This is just before sunset around 19:00. It was getting dark out and the ISO was cranked to 800 so there is some digital noise. This is the same 1/160 exposure time. She let me get a foot or two closer, which combined with the focal length to get a whole lot more bird and less plant in the shot.
But the kick in the teeth is the sharpness. This is a best-guess manual focus with a manual lens.
The focus action on this lens, by the way, is sexy. Like turning a metal cylinder in thick grease . . . oh wait, that's what is happening.
You can get a lens with a 15x zoom range and replace a whole bag full of prime lenses for everyday shooting. You can take award-winning photos with a kit lens even, given enough light. But when you really want sharp, sharp, sharpness in your focus, it will fall behind a good prime.