We have to start with the explanation that the stablecoins are the most important and integral part of the cryptocurrency industry and play pivotal role. On the other hand not all of them should be treated equally. We are usually switching to them if we are expecting worsening market conditions (i.e. going from the bull market to the bear market). It is one of the good metrics to analyze the cryptocurrency market. It is one of the best place (I guess alongside bitcoin) where to hide. There are multiple option now between which we can choose the right stablecoin for our needs. Lot of them work on multiple blockchains so you can choose which suits you the best (it is important to choose between speed, fees, security and decentralization). On the other hand there are reasonable concerns about credibility and collateralization of the stablecoins. There are different types of stablecoins - algorithmic and pegged stablecoins. We have in memory how quickly algorithmic stablecoins can crash to almost zero (Terra stablecoins is a great example). Lets focus on the pegged stablecoins where is the main focus on the state of the assets used as a collateral - usually fiat currency (if it is stablecoin pegged to the American dollar, then there should be the same amount of the American dollars as minted stablecoins in the accounts of traditional banks with the ratio 1:1). There are some stablecoins which are collateralized by different cryptocurrencies or assets so there always exists risk of volatility and depegging. On the top spot as most stable and used are Tether (USDT) and USD coin (USDC), then follows Binance USD (BUSD). I would focus on most trustworthy stablecoins such us USDC and exclude Tether for now on. To make things clear the Binance USD is not minted by the Binance (there would be the risk of single point of failure) but it is minted by Paxos which is quite trusted company in crypto space.
It should be at least partially regulated and approved. It should be pegged 1:1 to American dollar with the reserves covering the amount minted. The American dollars used as a collateral should be stored with respected American banks.
At is the most important question is why Binance needed their own stablecoin if there is similar competition (such as USD coin mentioned).
I think it is mainly about the competition as the USD coin is closely connected to the Coinbase (competing exchange). That is why the Binance converted all the USD coins to the Binance USD to be able to look after their reservers in stablecoins and to be able to manage the liquidity. I think it was a quite smart move.