user17010: For what do you need to know the number of full moves? You still can't recreate every move in the game with FEN anyways, so I don't see the point of the full move counter. Is there any rule that depends on it?

user12629: One rule that depends on the move count is the time control.  If you have a time control of 40/120, you need to know which move it is to know when the players get more time.

user3456: You may want to record a fragment of a real game starting from move number 24, for example. Then you specify the FEN after the first 23 moves and set the full move number to 24.

17010: <p>For what do you need to know the number of full moves? You still can't recreate every move in the game with FEN anyways, so I don't see the point of the full move counter. Is there any rule that depends on it?</p>
 12629: <p>One rule that depends on the move count is the time control.  If you have a time control of 40/120, you need to know which move it is to know when the players get more time.</p>
 3456: <p>You may want to record a fragment of a real game starting from move number 24, for example. Then you specify the FEN after the first 23 moves and set the full move number to 24.</p>
