This initial stage sets a tone for scope, vision and procedures that come to fruition later in the project.
The discovery or planning stage is the part of a web project where a project manager defines what they plan to achieve and how their agency will achieve it. Planning reduces scope creep and helps set expectations with clients. Additionally, in this planning stage, project managers have a chance to understand the underlaying business goals of a project--an insight that makes a project more successful and impactful for an organization. There are some agencies that spend 50% of a projects scheduled time and budget within this initial phase.
Certainly, there are clients who wish to skip the planning and discovery phase, seeing it as a waste of time and resources. Often times, clients may begin a project by saying they "already did the planning and wireframes necessary." It is vital that the project manager and agency persuade the client to invest in a proper planning phase to establish a baseline for the project--clarifying intentions, content needs and strategy. Simply reproducing wireframes does not help an agency understand the logic and intent of those planning documents. If you cannot persuade the client to allow for a discovery and planning stage, then it may be worth reconsidering working on that project.