Today's rule interpretation

The first principle of Officiating

"The purpose of the playing rules is to penalize a player who, by reason of an illegal act, has placed an opponent at a disadvantage."

This principle is the fundamental rule of Officiating. Every penalty decision made by an an On-Ice-Official (whether to call, or not to call) is judged on whether there has been both: an illegal infraction as per the rule book, and a material change in advantage to one team.

The purpose of this principle is to ensure that the game progresses smoothly and so that it is not unnecessarily interrupted by the official's whistle.

Source: NOCP Participant Manual