Each time you make a contribution or a withdrawal, the money will be allocated to help you reach your original target allocation.
Let’s say your target allocation is 70% invested and 30% in cash. If you contribute $100 to start off the account, $70 will be invested. Over time, that investment could grow to be $80. Now, your total balance is $110 and your allocations are 72% invested and 28% in cash, because an investment can grow quicker than cash.
In this instance when a contribution is made, money will be added to the cash option first to help it go back to 30%, and the rest of the money will be allocated based on your target allocation. The same thing happens when you withdraw money. The goal is to maintain your original target allocation.