When you perform tasks for your allegiance leaders, or kill monsters inside enemy allegiance dungeons you gain allegiance points (AP). These points are cuumulative so you can gain them freely without any limit. Aside from ranking purposes the purpose of these points is to allow you to access two allegiance features.
Track Outposts
World > Track > Outposts
This feature lets you track enemy outposts (used with sieging to gain AP). There are outposts in the second realm and higher, but not the first.
Track Enemies
World > Track > Enemies
This feature lets you track players in opposing allegiances, for every 5 AP you can track 1 physical level, this means with 500 AP you can track up to level 100 players.
Essentially the higher your AP the more you can track, so go out there and do wonderous things for your allegiances!