The Edge is a reference to the "small things" that separate the best photographic equipment from the also-ran stuff.
What things give you an 'edge', photographically speaking? This is a tricky question to answer. Some of the things are surprisingly dull, like a good incident flash meter, a tape measure, a book of photographic calculation equations,some basic mathematics theory and practice,and some theoretical understanding of the principles of light and exposure,as well as some art study and some design and composition study. Other things are exciting products that are for sale at the photographic equipment retailers in the USA and Europe and Japan. You know, stuff like tripods, lenses, flash gear,and so on.
One thing that gives you an edge is a clean lens,front and rear. Today's microfiber cleaning cloths are superb compared to the old-fahioned standbys like Kodak Lens Cleaning Tissue or a freshly-laundered 100 percent cotton T-shirt or an old-fashioned lens chamois. There is nothing that can hold a candle to a good,new microfiber lens cleaning cloth.
A quality prime lens, like a 50mm 1.8,85mm 1.8, a 90- or 100- or 105mm f/2.8 macro lens, and a 300mm f/4 prime lens are four specific lens categories where owning a lens in each of the four categories can at times give you an edge over people who do not posses those specific lenses. You NEED a 50mm normal lens, you need a short macro telephoto,you need a high-speed short 85mm or 100mm f/2 or faster telephoto that focuses WELL and is sharp even wide open,and you need a prime 300mm f/4 lens. You might wonder why you would want a short macro telephoto AND an 85mm or 100mm f/2 or faster lens. Trust me, the short telephoto macro and the 85mm 1.8 or 85mm 1.4 lenses are different animals, and a 100 or 105mm f/2 or faster prime lens will be a real honey, no matter which brand you shoot. The 300mm f/4 prime lens, like Nikon's AF-S model is a very,very sharp,compact telephoto with many,many years' worth of service built right in. It's worth the thousand dollars. It shoots well,carries well,and makes pretty pictures. Nikon's 300mm f/4 AF-S lens is an investment.
A 12mm extension tube gives you an edge. The 12mm length tube is the most-useful length,followed by something around 20 to 24mm in length. The Kenko brand of AF, as in autofocus, extension tubes is available in single lengths,as well as in 3-ring sets. Similar producs have been marketed under other brand names in Europe,such as Soligar AF extension tubes. Pair the 12mm tube with the 300mm f/4 telephoto,and you have a good macro-range combo for skittish subjects or botanical gardens,etc.
A working,workable electronic flash diffuser unit gives you an edge. There are many,many types of devices that diffuse,or bounce, or bounce and diffuse, shoe-mount flash units like the Nikon SB 800 or Canon 550 EX flash. Lumiquest,Sto-Fen,Gary Fong,Photoflex,and other brands sell devices which MODIFY the output of a shoe-mount type flash. Mini-softboxes from Photoflex for example, can be useful; the Lumiquest bouncer devices have adherents, the original Sto-Fen flash diffuser has been SO successful that Nikon has included one of its design with every SB 800 flash sold,and so on. What is needed is some type of device that works for YOUR use of electronic flash. And to go with this, you NEED, you absolutely NEED a TTL remote flash connector cable, like the Nikon SC-29 cable for the new cameras and new flashes. Get the flash out of the shoe,put it in your left hand, or on a bracket,and learn how to point the flash around with the left hand when it's actually useful to do so.
A solid monpod gives you an edge. It really,really does,if you know how and when to use it. it helps keep you framed up when using long,heavy lenses, yet gives you flexibility and mobility. A monopod can also help you make very slow-speed wide-angle pictures in dim,crappy lighting, and it also steadies short telephoto lenses like 85-105-135 very,very well.
One of the big pro-type lenses can give you an edge. The AF speed and surety of the pro-glass lenses from Canon and Nikon,plus their uncompromised optical excellence and quality brings images with rich color saturation,high resolving power,good image contrast,and high quality imaging characteristics. The 200/2 VR and 300/2.8 lenses come to mind, as well as the 400,500,and 600 AF-S Nikkors and the 200-400 VR Nikkor. Smaller, more-modest and much more-afordable 85mm 1.4 or 105 DC lenses and the 70-200 f/2.8 stabilized telephotos also would qualify as lenses which "can" give you an edge when comparing what these lenses can do compared with the kind of results one can get with typical consumer-grade lenses. If you get into photography long enough and seriously enough, you will discover that there ARE a FEW lenses which can give you a real,true edge over those that are shooting wthout benefit of similar, state-of-the-art optics. The modern, 300mm f/2.8 telephoto class is a good example of a specific length and type of lens that has superb color saturation, superior image sharpness and contrast,and really first-rate AF performance,and which simply works BETTER than anything made at this time, for some situations. Nikon's 200mm f/2 VR is another similar lens which brings with it an edge over say, a 70-200mm f/2.8 lens.
The real issue for serious shooters these days is to realize that YES, there ARE pieces of equipment that can and will bring with them a real,decided EDGE over shooters who do not have access to the same equipment; the problem is not in accepting the above fact, but in finding the financing to float all the new gear!