Photographers struggle mightily with finding a suitable camera bag. Eventually most photographers will come around to the Photo Vest. But before you purchase a vest you may want to consider the following. The photographers who most commonly use a vest are those who are shooting sports or press events. These photographers are on the go, moving from one location to another. The vest is perfect for this because press photographers often have to change lenses or add a flash on the fly. They also have to get to notepads and pens or other recording devices as well. A jacket allows very fast access to all of your "stuff", provided that you remember which pocket it lives in.
So what's the downside? First, heat. Vests tend to be very warm so using them in warmer climates is not ideal. On the other hand, if it's cold out you will need to put it over your jacket which means you will need a larger vest than the one you used in moderate weather conditions. What about rain? Vests are generally not waterproof whereas most camera bags offer a rain cover although poncho over a vest would certainly work better than a poncho over a bag. Another downside of the vest is size. If you are a smaller person you will have to wear a much larger size to insure that everything fits. Why? The pockets on vests are sized according to the overall size of the actual vest and not your equipment. Therefore a vest designed for a tall man may accommodate the 70-200mm f/2.8 lens but a small vest for a woman will not. Unfortunately, your equipment is not smaller just because you are.
Aside from comfort there are other issues with a vest. If you are using it while traveling, what will you do when you have to sit down for lunch or get into a car? The largest pocket on a vest is normally the one on the back where you would store a 70-200mm lens. Imagine sitting in a cab with this next to your butt. A photo vest is meant to stow all of your photo needs except for the camera which means that your camera is always out; there is nowhere to store the camera while having lunch or if you are walking through a museum that restricts photography. Also if you are traveling, you will need to pack everything in a bag for your flight and then switch to the vest on the other end. This means that you are packing more things in your luggage or carry on. As you can see there are some definite benefits and limitations to a photo vest.