Using this feature, a player can have up to 4 parties available for any Fight; every player begins with 2 of these Party slots available. Being able to change decks is incredibly easy to do and convenient for saving time, effort, and mana.
The first step is to create your strongest party (used for fighting in Arenas and Raids) and save it in the first open slot, naming it appropriately. Then, simply edit your party to a "Current Party" to be used for questing, entering Arenas, or any other function. You can purchase additonal Save Party slots for gems.These saved parties are able to be loaded back to your current party for editing, or you can replace them with new parties you create.
One of the many ways this management is helpful is when lowering your Arena deck in order to benefit new or weak players joining the game.
Start by entering the Arena with a low deck...
Here, you can see my Questing Deck has entered the arena.
Then you can switch between your saved decks using the arrows under your deck photo.
...until you get the deck with which you wish to battle!
When other players enter the Arena, they will see your lowered deck instead of the higher one, allowing more new and weak player to benefit from the MIght rewards in the Arena, and allowing everyone to spend less time or gems waiting to reload new battles!