Yes , you need a filler and or panel .

1. You need something solid to attach the fridge to, and drywall isn't going to cut it. You don't want that puppy tipping over on you, trust me. I've see it first hand.

2. If you have a handle on the fridge and you have no filler the handle is going to hit the wall and not allow you utilize the pullout drawers as well as buggering up the wall.

The filler needs to be at least as wide as the handle projects from the door face. More is better.

You need a filler not just for the handle but for the door. The door swings out beyond the side of the refrigerator when opening. If this is against a wall you will not be able to open the door beyond about 45 degrees.

I have 3" of filler between my wall and refrigerator column. I would imagine that is required as detailed above.

I would recommend going to the Thermador website and downloading their planning design guide.

http://a7ced1f75a02a100d3a2-90d763fcf9b92a01a2bbdc9048c20c84.r80.cf1.rackcdn.com/Refrigeration-Freedom-Collection.pdf

Was the 3 inches enough to open the door to 90 degrees?