FreeDrive is the driving mode in which you can drive freely, when not doing participating in any event (like missions or skills). You can, however, trigger those events when approaching the appropriate locations while in FreeDrive.
FreeDrive is the only mode in which you can gain by doing stunts. Some awards can also be granted only in FreeDrive. In FreeDrive you also do all the exploration for landmarks, data stations and kit cars wrecks. FreeDrive is also the easiest mode in which you can uncover map allowing you to fast travel to uncovered places.