We suggest to all developer plugins, use $player->getId() instead $player->getName() as array index / cache. That will make low memory usage and high performance.
He is correct saying as each letter takes 5 bits and each number only takes 4 bits. Its not a drastic change but it will definetly help with performance if you have a mass amount of players on.
Two rookie mistakes are using names as identifiers and not using Player::getDisplayName() as display name.