Many times I see students of mine compose a picture in which they inadvertently cut off the tip of something, such as a wing, an ear, a hand, a foot, a tail, etc. This is not a good idea. If you want to crop a subject in-camera or in post-processing, do so decidely. Otherwise include the entire shape of the subject. This buckeye butterfly, for example, would not look good at all had I clipped one of its wings. That would have been injurious to the picture because our eye would go to that area immedately and return again and again, and that's not what you want. You want the eye to stay focused on the main subject, not on a peripheral element in the shot.