What are the advantages in making spousal maintenance non-modifiable?

Spousal maintenance is only modifiable by agreement between you and your spouse. The effect of the agreement is to remove all jurisdiction from the courts to modify spousal maintenance at all. The advantage is that you litigate spousal maintenance, which can be a heavily litigated issue, only once. Once spousal maintenance is made non-modifiable, it does not get revisited. And you are only back in Court if the paying spouse fails to pay.