A recent Delaware supreme court holding might motivate contract drafters to define the term for themselves
If your client is going to contractually commit to using "commercially reasonable efforts" to do something — but expects that obligation to require something less than “all reasonable efforts” — then you’ll want to make the client's expectation clear in the contract language itself. Otherwise, if a court were to follow a recent trend in Delaware case law, the court might judge your client's performance against an all-reasonable-efforts standard.