If you are shooting insects or live ‘whatever’, some lenses
require you to be so close to the subject that the end of the lens
actually blocks the light or the close proximity of the lens scares
off whatever you are photographing. The 60mm range of macro
lenses are in this category. And while the 100mm to 105mm
macro lenses are very popular, many photographers would
rather work with lenses in the 200mm range because it gives
them just enough extra distance to not disturb their subjects. If
you are really into photographing critters then a lens in the
200mm range may be what you are looking for. When you get
to longer telephoto lenses then you want a close-focus
distance, especially if the lens is not a macro lens.
One odd technique I like is to use a telephoto like the Nikon 300m
F/4 ED-IF lens (which has a minimum focus distance of something
like 4.9 feet) on the Nikon D3x (which has 24 MP) and crop out a
photo. I can photograph a frog out in the middle of the pond, crop
it out, and still have enough pixels left for a fine photo.
Close-focus distance for many lenses is listed in the second
volume in this series "Lenses for Close-Up and Macro
Photography."