To my knowledge, a legally binding contract is between two parties and I have learned that putting agreements "in writing" or "documented" is always the safest medium to avoid any inconveniences, false accusations or abrupt challenges . For instance, as a listing agent, once i've helped a client sell a property or land, we must state it in the contract or agreement that I am to get a commission for my marketing or listing expertise once that deal is successful(closes). With the written agreement in place, this will protect me as the agent once there are any disrepancies on the seller's part as previously mentioned. The key takeaway is that, having everything documented helps all parties involved to "hold their end of the bargain" from the beginning, therefore if any future challenges arise, then we can always refer to the agreement to settle the matter.