I believe if you are enrolled in Instant they will spot the money for any purchases you make beyond the amount you already have in your account, up to $500 wort

I believe if you are enrolled in Instant they will spot the money for any purchases you make beyond the amount you already have in your account, up to $500 worth. So it just enables you to use Dwolla for purchases without having to wait for a slow ETF transfer (around 3 days) from your bank to fund your Dwolla account.