Once a basic color is determined, now comes the fun and creative part. She may suggest adding lighter highlights around your face and maybe even dispersed throughout your hair. Lighter color near your face can change your entire appearance without the permanent commitment of an all over change.
Plus few things offer the opportunity to change your look the way changing the shade of your tresses does. It lets you keep everything else virtually the same while still giving you the change you seek. Not a bad deal actually.