I do not think Golovkin will ever have to worry about paying the bills with what he has made. Of course he'll still want more and thus from a financial standpoint he much to gain fighting Canelo.
As for a legacy standpoint beating Canelo will help Golovkin but this is more about Canelo now. He has damaged his legacy with the PEDs. He needs to beat Golovkin to help him redeem his legacy. First in most people's eyes he lost the first fight, then they find out he was likely cheating. He has much more to gain now beating Golovkin than Golovkin has beating Canelo.
As for a legacy standpoint beating Canelo will help Golovkin but this is more about Canelo now. He has damaged his legacy with the PEDs. He needs to beat Golovkin to help him redeem his legacy. First in most people's eyes he lost the first fight, then they find out he was likely cheating. He has much more to gain now beating Golovkin than Golovkin has beating Canelo.

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