Joining IEO remove's the risk of holding a bag of worthless tokens compare to traditional ICO.
With IEO all investors are secure that they can freely liquidate their bought coin after the IEO sale. While in traditional ICO it carries a heavy risk that the token/coin might not be listed on a exchange.
I don't quite agree that IEO guarantees the investors of coin liquidation after the sales. What if the coin gets listed and yet the investors gets to lose a better part of their investment. For me, the only advantage of IEO over ICO is just that the coin gets listed after all, but it doesn't guarantee the success of the project except in few cases of IEO conducted in a good and reputable exchange like Binance, Kucoin, etc.