The untainted pool might have been there to give Rand more time before the taint overcame him. If you consider had the pool not been there and Rand was able to channel enough to destroy as much of the trollock army as he did and then fight Ishamael how much taint would he had brought into his system?

I doubt if he would have gone mad there and then but if you think of it as accumulated damage those extra damage points from the taint he would have been exposed to added to what he got from channeling as he did after that could have meant he decided to end everything is say PoD or before he could cleanse the taint in WH

Likewise if the pool had not been there Rand would not have gone to the Blight would not have fought Aginor or Ishamael or would not have been in a position to save the borderland army. Why? Because if there as no Eye Rand would still have been knocking around Andor.