Question for fenderwell header guys/gals

If the engine/trans are out, all suspension gone, and front of car is supported by jackstands at the rear of the front frame rails, I don't see why the frame rails would move when the inner fenders are removed. At any rate, I once had fenderwell headers in my 65 Barracuda. Decided to get rid of them. I drilled out the spot welds holding the inner fenders on this car and my parts car, then welded the good inners onto my car. Been back together now for thirty years, no issues that I've ever noticed. 340/4-speed car.