They needed a consultant; you needed a client. You pitched them, met with them, cooked up a proposal, negotiated and closed the deal. Now there's only one thing left to do: prepare and sign a contract.
Why bother? For one thing, according to movie mogul Samuel Goldwyn, "a verbal agreement isn't worth the paper it's printed on." Often, consultants are vulnerable to the whims and "convenient" memories of their clients. It's not that oral agreements aren't legally binding--they're just much harder to prove.
There's also a more subtle benefit to writing things down--it makes you think. Putting pen to paper forces each side to be specific about its expectations and more thorough about planning for problems. In fact, Glenn C. Devitt, co-owner of Isotope Media, a homebased Web marketing and design firm in Plainsboro, New Jersey, sees the formal agreement as a chance to produce good will. "Before accepting a signature from a client, we sit down with them and discuss the details of the agreement, line by line," Devitt says. "Clients appreciate this step, particularly because we often deal with individuals who are unfamiliar with the language and intricacies of our profession. Reviewing the contract is an additional opportunity to educate them about what they're getting into."
Finally, people sign written documents as a symbol, to memorialize the handshake that says "We've got a deal."