It was mainly the bears saying the futures would increase shorts on bitcoin.
Can't imagine anyone in their right mind would short bitcoin right now though...
This is useful for instance for a fund that needs to neutralize its positions while closing them over a span of several days/weeks. If you expect a future payment in BTC and don't want to expose yourself to the risk that Bitcoin will crash: you short the equivalent amount in futures.
Because futures contracts are (usually) much more liquid that actual assets, they are very useful to short whenever you have the actual asset in your books and don't want to expose yourself to the risk of it losing value.
Not sure if I'm explaining all this very clearly...
Why not? I can't believe anyone in their right mind would significantly invest in Bitcoin right now.
You would have to be completely nuts to short it, regardless of what you think it is going to do in the medium-term.