Increase Your Zooming Power Through Resolution
Shooting at your camera's highest resolution offers you many benefits, including the ability to crop an image to provide the illusion that you were closer to the action than you actually were.
For example, if you're shooting pictures of birds in flight with a 3 megapixel camera, then you will have plenty of resolution to crop in on the original shot to make the main subject appear larger than it was in the camera's viewfinder.
If, on the other hand, you were shooting a lower resolution, such as 640 x 480, then you wouldn't have enough resolution to crop and still have a decent sized image.
Always shoot at your camera's highest resolution so you have the option of cropping if you need it.
The original image just doesn't have the impact that you want because your lens wasn't powerful enough to bring the subject as close as you wanted.
But, because you shot the picture at your camera's highest resolution, you were able to later crop the image to make it appear closer than it really was.