Anyone who's worked on a web project knows about scope creep. No matter how well-defined the scope of a project is in the beginning, chances are the scope will change between kickoff and final delivery. "A List Apart," the popular blog for web developers and designers, recently published an article on the wisdom of conducting up-front user-centered research to determine scope and develop a Request for Proposal (RFP) that can be put out for bid.
Getting input from lots of users, both internal (the people who administer and post content to the site) and external (the end users), helps guide sound decision-making, reduces scope creep later on and provides a great way to "show your work." When someone asks you later on why you designed the User Interface (UI) a certain way or how the site functions, you'll be able to point to thoroughly-vetted user research as the basis for your design decisions.
This type of research balances scope with budget. It will become clear right away if users are asking for champagne or a pilsner budget. All parties will be happier - client, designer, developer and users - if expectations are managed on the front end.
This type of user-centered research naturally leads to a solid definition of scope and ultimately an RFP that can be put out to bid. So before jumping in head-first, talk with user-centered web consultants to get your project off on the right foot.