I am a great believer in the desireability of uniform center-to-corner
performance so that I am not limited to one photo type. If I shoot, I want
the tree branches in the corners, the water texture, the grass or rug or
field foliage texture, etc. to be sharp - a photo's subject IS NOT the
object that is planted in the middle of the frame, it is EVERYTHING
within the frame (it all has to make sense as part of the photograph,
and contribute to the image). If corners are uniformly soft, all photos
have a definite characteristic which may not be appropriate for many
types of photos - kinda like saying its OK if your new car has crumpled or
missing corners, since you don't need them anyway....(though that condition
DEFINITELY affects your perception of the car [and its quality level],
and may even affect how you drive the car!). Same with a photo - if there is
a consistent deficiency like a lack of a black tone, unevenly sharp grain
in a black-and-white print, uneven illumination, unsharp corners, etc. -
we would consider the photo to be deficient in an important way (this, of
course, is not absolute - the requirements of a particular image may lead
one to choose to use any of the "defects", if it is appropriate for the image).
So there! ;-) David