In close-up photography, one of your biggest goals is to draw attention to your subject–you want to make it really stand out.
One way to make your subject out is to make it the sharpest part of the image, since the viewer will usually look at the sharpest thing first.
Marco or close-up photoraphy, a strong contrast will make for better results. Learning the best spot on your lens, or the aperture will find you with the clearest point.