4 good reasons to buy a pancake lens

From Andrew Gibson at Picture Correct:

1. Simplicity: Pancakes are prime lenses. From an optical design point of view they are pretty simple, much like a 50mm prime lens. The Canon 40mm pancake lens has six elements, whereas zooms usually have ten to twenty elements. This translates to high image quality and lower manufacturing costs.
2. Price. Pancake lenses tend to be inexpensive. You get a lot of bang for your buck in terms of image quality.
3. Aperture. The maximum aperture of my 40mm pancake lens is f2.8. This is not especially impressive for a prime lens, but better than most zooms. If your main lens is a kit lens you will certainly appreciate the improvement.
4. Short minimum focusing distance. The 40mm pancake lens can focus on a subject within 28 centimetres of the camera. This is quite close, and you can get even closer by using extension tubes.