I don't think that any trader will ever use that tool for trading. The fees on Binance spot trading aren't much high and if someone can trade with a proper trading plan and well developed strategy the %age of earnings are much higher compare to that minimum fee. Spot trading offers many functionalities that the convert function doesn't allow. No good trader will give up on those features.

Convert function is only useful if you have small amount of a coin that you want to convert into a stable coin other than that I haven't found any good use case for that function in trading. Even if it doesn't have fees directly, but your conversion will be executed on higher price than the current market price so the exchange can earn their share from the conversion.