When you think of the game as a PvP Arena, then there is no benefit to ranks at all. You could start playing as an Academy Student and somehow grind to level 100. The problem with that is the main way to level up is to do missions. Missions not being repetitive grind missions, but actual storyline missions and with actual content. There will be a certain amount of Arcs for each rank in the game. So each Genin at his end of his time as a Genin, going to participate in the Chunin Exam will be roughly the same level, because that's as far as the missions progressed him, unless he took a hell load of time to grind up extra levels, but seeing as how mobs will give very little experience, this will be hard.