Yes I think that there is a difference between a verbal and a written contract. A written contract can be more in depth where one party will take more time and room to outline some rules, agreements and restrictions in the contract. The written agreement will also be there forever, where both parties can go back and look at exactly what they agreed on. In a verbal contract words can be misperceived, and when arguments happen or when one party wants to bring in the legal system a written contract will be much better to refer back to and defend ones original claims. Through lengthy written contracts more details can be set up to go over all necessities, rather than having a 30 minute verbal conversation where both parties agree at the end. Verbal contracts can lead to untrustworthy people using you or turning back against their agreement to get the benefit of the doubt. I do not think you should start fully working on a project because of a verbal agreement because the other party can still back out or change things. You can start planning but I do not think actual progressive work should be done until a written contract is looked over and signed.