Yes- the opt out lessons the chances that the contract ends up being an under pay because if the player has a big season they leave, but leaves steady the chances of an overpay since if they get seriously injured or have their performance fall off a cliff, they will not exercise the opt out
I suppose I think about it this way: The end of the contract will be dead weight regardless of how the player performs for the first half. I see the last 3-4 years as guaranteed overpay. Anything that lessens the chance of the player being on your team for those years is a net positive.
Maybe I am thinking about this incorrectly.