- If he approaches the huddle and communicates with a teammate, he is required to participate in at least one play before being withdrawn. Violations of this rule may be penalized for unsportsmanlike conduct.
Note: The intent of the rule is to prevent teams from using simulated substitutions to confuse an opponent, while still permitting a player (or players) to enter and leave without participating in a play in certain situations, such as a change in a coaching decision on fourth down, even though he has approached the huddle and communicated with a teammate. Similarly, if a player who participated in the previous play leaves the playing field by mistake, and returns to the playing field prior to the snap, he is not required to reach the inside of the field numerals, provided that the defense has the opportunity to match up with him. However, a substitute (i.e., someone who did not participate in the previous play) is required to reach the inside of the field numerals.
Edit: everything above this is directly from the rulebook.
They are just quoting the part that makes them look good. It specifically says it allows for coaches changing their mind.