Let's assume you are entering a position using a TA in USD. Then you can use five volumes in $ "to enter" and five volumes in lots "to exit." It's easier to exit a position. After entering the market, the asset's price in $ will change, so TA in lots will allow closing the position completely.
Position "leftovers" can also be closed with an Alt button. Left Alt is a hotkey that allows closing the entire position with one click. It "inserts" the entire volume of the position into the order. For example, you built up a position with three purchases worth one lot each. In total, there are three lots. If your TA is set to one lot, then by sending a sell order, you'll sell one lot. It will take three sales to close the entire position. But if you hold down the left Alt and place a sell order, the order will include the entire volume of the open position (regardless of your TA).
The traded amount in $ can only be set for CScalp connections with Binance and Bybit.