There is a lot that goes into launching a Website, but it all boils down to the why. Who are your users, what do they need and how can you make it your business to deliver it to them? What do you want your users to see, how should they react, and what makes a successful site (In both your opinion and your customers). I believe good design is working with a measure twice, cut once mentality. Building on a solid process of deliverables to allow for alignment of expectations between all stakeholders to ensure success.
UX Designers have become somewhat ubiquitous across the design industry and that role's actual function has become muddled, meaning anything from simply a person who can both design and develop a website to someone who understands the goals of the interface. I believe it is someone who speaks for the user, making sure their voice is heard and understood. By building an interface that speaks directly to the needs of the user, any reasonable goal set by the client can be met.