What is the difference between a Profile and Role?
Roles are one of the ways you can control access to records. They also impact reports (e.g. "My Teams" filter). Roles come into play if your security model (OWDs) are set to private. A little more on Roles and how they impact security:
Profiles help determine record privileges. Assuming the User can see the record, Profiles determine what the User can do, view or edit on that record. Profiles control other system privileges as well (mass email, export data, etc).