You will incur brokerage when we have to trade (sell) holdings. We make trades for these reasons:
Creating your portfolio and buying holdings
Adding funds to your account and buying holdings
When rebalancing your portfolio, so it stays in line with the portfolio objectives.
Rebalancing may involve the buying of some holdings and the selling of others.
You are withdrawing funds from your account and selling holdings to free up cash for the withdrawal.
Closing your portfolio and selling all holdings