Those ranks would be of limited use for anything but internal use anyway. Even if a select number of places have standardized their ranking system by using the common exam. In that sense even knowing somebody's rank in battle has only suggestive value, if even that. To put in simply, like you said, they are convenient when dealing out missions and perhaps deciding troop compositions during wars. But they are useless when facing an unknown enemy.Originally Posted by RyougaZell
In fact, Naruto himself demonstrated this perfectly: Simply because he hasn't been in the common shinobi pool for a couple of years, he has had absolutely no use for a rank. Now that he's back, it does pose a problem for him (because he has always wanted the hardest missions available, but the rank of a genin wouldn't theoretically allow that).