There are some Nigerians that can use this to make money. In short, they are using it to make money.
For the fee, sending from Binance to OKX and some other exchanges can be though lightning network. Bitcoin transaction fee on OKX is one of the cheapest on exchanges. So from Binance -> OKX -> the destination exchange.
Converting to altcoin, send altcoin to the other exchange and convert back to bitcoin can be helpful, depending on the amount.
It looks profitable from looking at the screen prices but in reality is it not, in fact your always going to be at loss if you are thinking about running an arbitraging between OKX and Binance, i use two of these CEX and I've tried practically and it never worked. the average BUY price on Binance is low N23,845,772.55 as compared to the BUY price on OKX at average N28- 30,004,0027 but the SELL price on both are 23,500,461.19 or less. what does it means ?
It means if you buy from Binance at 23,845,77.55 and sell on OKX at 23,500,461.19 you are going to be in a minimum loss of about 3k +gas fees.
If you buy from OKX at 28- 30,004,0027.19 and sell on Binance at 23,500,461.19 you are going to be at a big loss of about 5-10k +gas fees.
So mathematically OKX and Binance arbitraging doesn't work. I don't know about other exchanges.