Why Unlimited Allowance

Turbine asks you for unlimited allowance to hide your sell amount.

TL;DR: The allowance is unlimited to hide the full sell amount of your order.

When placing an order, you include a signed Permit2 allowance. It allows the TurbineSettler contract to spend an unlimited amount of your sell token for the duration of your order.

When Turbine settles your order on-chain, it uses the allowance you signed to take your sell token from your wallet. All on-chain data is public, so the allowance also becomes public.

Turbine orders are partially fillable, so settlement can happen across multiple blocks. This is common with low-spread orders.

Your allowance becomes public when Turbine settles the first part of your order. If the allowance matched the exact sell amount, the remaining part of your order would become public.

With unlimited approval, nobody knows whether the settlement they saw on-chain filled the order fully or left an unfilled portion in the orderbook.

Turbine keeps your order private until it is fully settled, which prevents anyone from frontrunning you and gives you better prices.