I've come across this recently on two separate occasions:
1) I created a set of web vector buttons so they would be infinitely scalable. When the original version was not pixel perfect and you scaled it to extreme sizes (make the button 1500 pixels wide) then the end result would be that corners did not align perfectly.
Also cloning buttons to make different versions was a problem. If you do not have the original Pixel perfect then the clone may have blurred borders or slight misalignment is
2) I Wanted to print some very small icons on a business card/letterhead. When the icons were not pixel perfect they would look blurred in print. You really have to be careful To have as little as possible anti-alias along the main lines of the shape to get a clean print