Some business organizations will require that an owner or partner's spouse sign a written agreement that the spouse will not seek any financial interest or ownership or demand a valuation of the business or their spouse's interest. Even if there is some financial disclosure and knowledge of what is being waived and the agreement is even "notarized," while it may be helpful to the owner/partner to show the
"intent" of the couple, the divorce court is not obligated to enforce it as if it were a proper and formally prepared pre- or postnuptial agreement that meets all statutory requirements.
Business owners/partners often are trying to protect each other from the ravages of an angry spouse looking to drag the business and other owners/partners through the mud to determine value and perhaps off-the-books revenue. In the case of a licensed professional the spouse cannot become a "partner," but the business value can still be determined and distributed from the owner spouse's share.
These non-matrimonial business-prepared agreements as a condition of entry to the spouse that is or is becoming a partner may have no, some, or great value in the divorce case. Asset distribution requires a review of the facts of the marriage, which includes length, presence of children, ages of the spouses, the type of business, whether there is a pre-marital component, future outlook for the business, and so many other factors that would make generalizing pure guesswork.
The best protection (if that is what is sought) is to have a formal matrimonial agreement prepared whether it is a pre- or postnuptial agreement. The more money that is involved the more important it becomes to do this properly and likely with attorneys for both sides. Properly prepared agreements are much easier for the courts to enforce.