I think shapeshift and blocktrades accumulate capital and only go on the exchanges when the balance gets out of kilter. So they are not taking risks, they just are more liquid.

Hey! 

> Doesn't shapeshift and the likes dump it on the market automatically too?

When you say "dump", no they don't have an open sell order that just dumps it all. Most of these companies go in both directions, so they likely hold and hedge in a bull market, they also sell back to customers who want to buy. Every day or week, they probably settle on an exchange or sell large blocks to other companies. 

Also, they buy/sell dozens of pairs of even more immature currencies than Steem.

For a small seller/buyer it does not make a difference, however I never recommend keeping money at an exchange.

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.

Let me explain. All the simple instant exchanges mostly provide operations via Poloniex or Bittrex. Our service http://Changelly.com also do the same. We have deposits on exchanges and on our proxy wallets to make exchanges fast for users. For each exchange operation we make the hedge deal on Poloniex and take a small fee for this. You can have a look, how it works, and how do we calculate rates here:
https://steemit.com/money/@changelly/how-changelly-suggests-the-best-exchange-rates