Unlike the vanilla Dispenser, the Block Dispenser can do more than just place down blocks. The Dispenser has a larger inventory, with a highlighted slot, which shows its current selected item. When it is triggered, it will use that item or place that block. When a block is placed, it can be sucked back into the Dispenser when the redstone signal is lost.
It can suck in friendly mobs such as chickens and wolves.
It has a variety of other uses: