"Gimel Coins are known for their unique but strange powers. Gimel Coins were used as currency by the Elw. The Elw were known for their superior knowledge of alchemy, so it is not surprising that their coins would possess magical power."- book in Court Seim
Gimel Coins were introduced in Wild Arms 2 where their only use is to allow the player to continue if they lost a battle, but starting in Wild Arms 3 they gained the function of allowing the player to save in almost any dungeon. They existed until Wild Arms 4, which brought back stationary save points in dungeons in the form of break points and created a system where the player could continue after a defeat indefinitely instead of relying on an item.
Wild Arms Alter Code: F
In Wild Arms Alter Code: F, it's expressly stated that the coins were the primary currency of the Elw. In fact, those refugees in the Elw Dimension still use Gimel Coins as their currency. An Ex File key is also purchasable for 99 Gimel Coins in the Elw Dimension.
Gimel Coins could also be used as portable save point or to continue after the whole party is defeated, much like its function from Wild Arms 2 and 3. If the player chooses to continue, however, the EXP multiplier of the party is 0.0, meaning the party won't get any experience points from the battle.