In spite of the convenience offered by zoom lenses, here are a few important reasons to switch to primes:
1. Primes are MUCH lighter and smaller. If you haven’t used primes before you should do so and you’ll see how nice they feel. This can be an important factor when hiking or walking long distances with your equipment. This brings us also to reason #2:
2. Strangers will feel much less intimidated about you taking photos of them if you use a small lens. This way you won’t look like a professional photographer (this IS good).
3. Primes are much cheaper than high-quality zooms. For example Nikon 24-70mm f2.8 will cost you around $1600 while primes in this range cost between $300 and $400 (50mm f1.8 will only cost $120).
4. There’s no need to have all possible focal lengths. Professional photographers very often go for whole assignments with one or two primes. Also if you look at photos you take with zooms you’ll most likely notice that a majority of your photos is taken at two, may be three typical focal lengths (one will be very often at the low or high end of the range). With primes you simply zoom with your feet! If not possible (which it is in a vast majority of cases), you can always crop the photo on your computer. This is not a problem with cameras above 10MP even for large prints!
5. Quality: because of the way they’re built, primes have an amazing quality, rarely reached by zooms. Even then, a prime will always be brighter and so will give you more possibilities when shooting at night or if trying to get a low depth of field.
6. Primes are usually very well built and last forever. They have less moving parts and so will on average last longer than zooms. Focus is always lightning fast, too.
7. Primes teach you to take better photos! The need to zoom with your legs teaches you to be more creative when approaching a scene. You also learn to see with a specific focal length. This teaches you to look in ways you might not look if walking around with a zoom. This probably means you become less lazy as a photographer, I suppose.
8. If you use one or two focal lengths, your photos will not only tend to be better but will be more consistent and much nicer to look at as a whole album.
9. They are simply more fun!! (ok, this is not an objective argument..)