In grading student assignments, I found myself commenting on their use of unless the parties agree otherwise. I thought that I had already written something somewhere about this phrase, but evidently not. So here goes:
As a general matter, the phrase unless the parties agree otherwise is redundant. The parties could agree to waive, amend, or delete any provision in a contract, whether or not that contract says that they may. But if a party feels that it would facilitate negotiation of a given provision if everyone were reminded that the parties might agree on a different arrangement down the road, then by all means use the phrase.