Example 1:  This is a scaled down version of what comes off the camera. It is an 8x12 horizontal picture. Example 1:  This is the same photo, but it shows the dotted lines where it would need to be cropped for an 8x10 or a 16x20.  You can lose some of the shoe on the left person and part of the shoulder or the right person.  This one happens to be minor, some photos could be more.
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Example 2:Here is a scaled down version of a vertical shot that comes off the camera as an 8x12. Example 2:This is the same photo, but is shows the dotted lines where it would need to be cropped for an 8x10 or a 16x20.  You see here that the picture will still be excellent.  This is because the frame is not full, it has some turf space on the bottom and some extra space above the heads.

Example 3:Here is another scaled down version of a vertical shot that comes off the camera as an 8x12.

Example 3:This is the same photo,  it shows the dotted lines where it would need to be cropped for an 8x10 or a 16x20.  As you can see here, this picture fills the frame more.  You can see the dotted lines use to crop for an 8x10 and a 16x20.  You can see that in order to keep both heads completely in the picture, the feet had to be cropped off.  The dotted lines indicate where the actual photo will be cut.  I could keep more feet in this picture, but I would lose part of the head of the player on the far left.
This should not effect any other print size you choose, 4x6's, 5x7's, 18x24's and 20x30's should have no problem just resizing.