It saves the club money during the negotiation. You give the guy an opt out in exchange for less dollars in total contract value. The AAV of a contract without an opt out will be bigger than one that contains one. The AAV of a long contract will be smaller that that of a short one.
And you can insure a contract against injury. I am positive someone could write a policy for performance. But you’re right, I said imagine. Because it would take creativity to do it and i don’t know the insurance business. But if David Wright’s contract was insured others could be too.
Serious question, what is the actual probability of Harper not opting out after four or five years if it’s available? I’d say much less than 20% and probably less than that.
In this situation, it's not clear that it does save money. If Harper is literally just going to take the biggest dollar value (as rumored) or highest AAV, an opt-out does nothing for that. It makes a lot of sense when you're trying to separate yourself from another offer or two that's close to yours. Here, that doesn't seem to be the case, and $35mm plus opt outs is...well, just an insane combination for that player.
As to the probability of him opting out, it's hard to guess, but 5 out of the 6 players with opt outs available from contracts with AAVs over $10m that came due this offseason didn't use them, sticking several teams with bad contracts - Price, Melancon, Heyward, Yasmany Tomas(!), Andrus. Only Kershaw opted out, and he basically just took a 1-year extension for doing so after a lot of hemming and hawing about whether he would stay in or not. The previous year also saw high-value contracts with opt-outs unused: Wei-Yin Chen, Cueto (yikes!), Ian Kennedy (3 years and $49 million, no wonder he stayed in!), Tanaka (this one looks ok for NYY at least).
Granted, most of those guys are several years older and a lot more injured than Harper will likely be in 3 or 4 years, but it's hard to pin it as low as 20% given that history.