I'm new at this but I have this suspicion that the institutions are moving more stock, either in or out, by using calls and puts to make the transfers. Then they are using the futures and some day trading to move the price around. Seems like most market price moves occur overnight (actually early morning during the pre-market) with gaps up or down and then day trading tends to be steady to choppy.
Options allows them to pick their price to lock in profit. Then they also can collect on some option premium as well as some pick some profit off of the futures and the pre-markets.
By doing this, they can disguise their trading in certain companies without leaving the daily telltale exchange volume that everybody follows. They use exercise and assignment of options as their trading vehicle.
Anyway, this is my pet theory so far and I'll wait to see if anyone else thinks it holds water or not or if there is something that can be graphed to show this.