It really only distinguishes the application of a rule without any judgment involved. But, because so many people - mostly fans, but many coaches, too - think they know the rules, it also serves to let those folks know that the incident in question is covered by rule, and there is no judgment involved in the ruling.
Example announcement: “When the ball carrier’s helmet came off, the ball was dead by rule. Third down. Number 22 of State may not participate in the next down.” So, all those fans booing and coaches griping because the advance by the BC across the goal line after his helmet came off doesn’t count will know why.
Robert