There is such a thing as a hometown discount - it equates to how much value there is to the player in not having to uproot his family and start over someplace else. That has real value. And there are even RARE cases where a player will take less to help his team construct a winner (I think Brown in LA was on record as having done this - which actually only points to why Cally can, and will, expect more in an UFA deal), however they are the exception, not the rule.
Best case, you save 3-5% for the convenience of the player not having to move, disrupt the lives of his wife and kids, learn a new system and organization, break a comfortable routine, etc. But that's it.