What is the difference between Display & Reflectance Processing?

Reflectance is where the pixel values are a true indication of the reflectance properties of the ground. The ratios of different "colours" is true to the actual situation, for example, and this is important for applications in which the spectral properties of the surface are important, e.g. for algorithms. A "visual" product is one in which the imagery values are optimised for "eyeballing" the imagery, e.g. manual interpretation or presentation and where the specific pixel values are not so critical.