You can think of tiers just like you can a level. In any MMORPG games, you have levels, whether it be a skill, or your character's level. Just like that, we have the same thing here with Guilds! Each Guild starts off on the first level/tier. Players can work together in their Guild to raise money in order to be able to upgrade it. You have full control over what perks a tier gets. You can give them more Mob EXP, Mob Damage, Permissions, and so much more! Tiers are a great incentive for players to continue to work hard on your server and unlock all the perks they can!