Most retail stores will use accent lighting in at least part of the space because it draws attention to the things that need to be noticed: key merchandise lines. Proper accent lighting will physically illuminate a product or display and guide the eye there. Accent lighting serves another important function: creating variance in light levels and therefore visual interest.
Without accent lighting, it is very difficult to create an interesting, atmospheric space. Lighting within shelving units is also considered accent lighting, and it should be noted that research shows products are twice as likely to be picked up from a shelf when it has lighting within it than those without.