Each transaction is characterised by size as a percentage of TVL. The small transactions (sardines) simply go in or out of the three stablecoin vaults in the same stablecoins and amounts requested by the user. This is the cheapest way to transact. Medium-sized transactions (tunas) get swapped if the deposit is into the most overexposed stablecoin or the withdrawal is from the most underexposed stablecoin. This can be more costly than a sardine transaction if a swap needs to happen. The large transactions (whales) get deposited or withdrawn in a balanced way, from each vault, to keep the system in equilibrium. This is the most costly of the three in gas, since whales effectively execute a rebalance each time they deposit or withdraw funds.