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No company will provide you service without profit, whether you have profit or loss, trading companies will take certain amount of interest from you. We shouldn't worry too much about the amount of trading fee that is deducted because that amount is very small.
There will definitely be benefits behind the promotions given and see how the Exchange is doing even if they provide cheap fees or even free fees.
Of course, there will be conditions to be able to get free fees or discounted trading fees and there may be some events as well so that trading fees can be free.
The more users who register and enter the trade, the more profit the Exchange will get.
Indeed, the amount of fees looks very small for one transaction, but try to add up how many transactions are made for each trader and all users make active trades, this will be a growing profit and can provide more returns than promos made.
Below are some Spot and Futures trading fee comparisons for the top Exchanges.