If you have enough good cards you don't really need to run two force of natures, but both force of nature and savage roar are good enough cards to play solo when you're in a pinch so it's not bad to put in double. I got rid of one of each so I could get two spider tanks into my deck, and I'm having a way easier time. Using force of nature to get better RNG on triggering an enemy sylvanas is also pretty decent.
Also, either card can potentially burst for a win even without the combo, because force of nature leaves enough mana for a swipe or keeper followup and savage roar works with anything on the board.
I got rid of my druid of the claws, though. At 5 mana I'd rather play belchers/loatheb or innervate out an ancient or Dr.Boom, and it's not that efficient at being a charger or a taunt.