Personas and Scenario Planning are tool to assist distinguish what a user requires.
They are the foundation for the look and feel of the design at the conclusion of the process. Personas are fictional archetype users. It helps in faithfully record and articulating who a specific archetypical user is, hence making better design decisions.
A scenario is a narrative describing possible interactions of types of users and systems. They include information about goals expectations, motivations, actions and reactions. They are not predictions or forecasts, rather they try to reflect the attempts the portrayal in how structures are used in everyday living.
Reflection
Personas and Scenario Planning are esential to the design process because it determines who is the design is catered for. Thus ensuring the design will meet the users needs.