I tend to agree that from a Steem price perspective, this is more important for someone who wants to sell a lot of Steem versus someone who is selling 100 or so Steem. It's very important for someone who wants to sell a lot of Steem to do so very carefully to avoid depressing the price during their selling or they will experience a significant loss during their trading (and also cut the value of their remaining holdings), and the instant exchanges tend to be better equipped to do this efficiently.

The advantages for the smaller seller are more in the safety and convenience associated with the use of an instant exchange. Unfortunately a lot of traditional exchange users find themselves ultimately leaving a lot of funds on that exchange, only to eventually experience a painful loss when the exchanged is hacked and they lose funds. I've personally lost funds through exchange hacks on four different occasions, so this happens a lot more than newcomers to crypto realize.