Simply put you will sell all your items through the World Auction on your alt character and keep stockpiling without upgrading much. Then when the time comes that you have a high amount of Garnets you will then buy some of the more high priced buyout items from your Main Character that you do not need. 

Towards the later game regarless if your server is dead or thriving with an abundance of players. Gear shortages are a real thing and through the ability to use alts we can farm specific gear catered to our class and then sell it back to our main to be able to take care of those tedious Evolutions, Gear Crafting and Potential Upgrades that seem to always want more and more. If you are planning to do this and do not plan on switching to another class, you will want to create 3 alt charecters of the same class to increase your gear yield.

When it comes to PvP we all need any kind of boost or advantage on the competition. Why not use your alts? Specifically a Dark Wizard and an Elf! They both can provide party buffs which will allow you to go into the Arena, Luprecal or any PvP scenario with increased Defense, ATK and a barrier...on TOP OF YOUR BARRIER!!!

I will say that you must be in a party with these alts so you will need 3 separate accounts to be able to pull this off but if done successfully as you may have seen in some of my videos then you just might have a chance to walk away with a few more wins!