Yes it's necessaru because your going to want to lower the engine down in order to get a wrench on the belt tensioner bolt. You could use fit a swevil head possible but it's really tight, also getting a torque wrench on their is impossible (40ft lbs).

After you've removed the top engine mount / torque strut mount (which is the mount on the bottom left side), you're going to want to wedge a piece of wood between a jack (scissors jack works) and your oil pan for support. That way you can dip the engine down and raise it later on.