What is Macro Photography?
"Macro photography" is simply another name for "close-up photography." The closer you can focus on your subject the larger it will appear in the frame, which is the point to macro photography -- to magnify small objects. Some purists insist that the term macro be reserved for images that are at least life-sized in the film -- an object 1" long must record an image 1" long or longer in the film to count as macro to these folks.
I prefer to speak more loosely of macro photography as being anything that uses some sort of technique that yields an image more magnified than would be possible with just an ordinary lens on the camera. For me, macro photography can have relatively small magnification factors -- just as long as there is more magnification than with a conventional lens by itself.
By the way, some people use the term "micro photography" instead of macro photography, but it's the same thing.
What is it good for?
Macro photography lets you fill the frame with small subjects. A picture of a caterpillar taken with a 50 mm lens from 10 feet away is likely to be uninteresting because the subject is a tiny speck in the photo. Make that same caterpillar fill the frame of film, however, and you've got an exciting photograph.
But you can do more than simply enlarge small subjects to fill the frame. You can use enough magnification to overfill the frame with the subject, abstracting out one part of the subject to stand for the whole. With enough magnification, you can make the photo an interesting abstraction where the viewer can't even tell what the original subject was. The possibilities of macro photography are limited only by your imagination.
Read further: http://www.edbergphoto.com/pages/Tip-macro-tools.html