Mapping out how a user will journey though your product or website and creating simple sketches (wireframes) problems can be quickly identified and fixed without needing to go through multiple teams and disciplines, therefor avoiding costly changes and fixes later in the project.
User flow diagrams can be used to map out new features or an entire project. Usually starting with the first point of contact (homepage, landing page or marketing material) through to completing the task they set out to accomplish and beyond. User flow diagrams usually take the form of a flow chart showing the connections between all of the pages or interactions your user can take through your product or website.
The main goal of wireframing a product or website is identify how a user will use your product to accomplish any given task. Usually consisting of sketches or simple diagrams wireframes can be quickly created and strung together to produce a low fidelity prototype. Wireframes are usually an extension of user flow diagrams showing a visual representation of the pages and touchpoints identified in the user flow diagrams.
Personas play an important part in both of these steps. Mapping out a users journey is much easier when you have a persona to map against, if we know the goals of your users, their frustrations and technical skill level we can design to fit these personas, meaning it is less likely that users will become frustrated when using your product or website.