If you stay within the Apple ecosystem like they really want you to, then you don't need that because your thunderbolt display has an ethernet adapter as well as some extra usb ports. The Apple monitor is their replacement for the docking station. Power and connectivity, as well as a place to put the laptop for reasonable space efficiency.
You don't need the thunderbolt adapter, but if you want gigabit Ethernet it's either thunderbolt or USB3 (as you mentioned). One of the perks of the thunderbolt adapter is that it doesn't require any third party drivers, which tend to be hit or miss with the USB3 adapters.