So it makes sense to save all your SD if you think that steem price will go down. And on the other hand, if you happen to have steem and think it might go down, it makes sense to buy SD with it. That can be done easily and for free in the internal exchange. This has one really big advantage: the money stays in the ecosystem. Users don't need to sell it for bitcoin so it doesn't affect the price.

Now that I thought a little bit more about this... Of course it will affect the price if people are selling Steem. It signals the markets that people value SD more than Steem. But it doesn't directly have effect on BTC/Steem-pair where probably most witnesses are getting their price information.

Anyway, it's great if the money stays in the ecosystem. This doesn't happen when people sell their Steem for BTC. It will be also interesting to see how much traders are going to use SD/BTC markets.