The logic behind it (which isnt all that sound given the reality), was that you would get 3 plays that were not being rushed (or hurried, no pun).
If they had ran on 2nd down and didnt make it for whatever reason, they wouldve used their last time out. On third down you run again and dont make it, then you are rushing the 4th down play and it would be chaotic racing against the clock with no way to stop it
i know Lynch would have scored most likely given 2 tries from the one yard line but

Carroll was probably just overthinking it