If our notation and rules of manipulation are limited, some things will be easier to express than others, and some manipulations will be easier to perform than others. Many familiar examples: arithmetic in Roman vs Arabic numerals; finding words or meanings in a dictionary vs a thesaurus; different types of filing system, whether paper or computerised; random access to casettes vs CDs; DNA is easier to copy, but protein is better for controlling synthesis; the effect of cutting up a photo vs a hologram; keeping track of position in a queue by holding a numbered ticket vs by standing in order; calculating the number of days between two dates written in d/m/y vs day-number notation; calculating the month of a date written in d/m/y vs day-number notation.
In general, a good representation allows you to express the information needed for the task being performed, in such a way that it can easily be processed by the operations you have available. See page 24 of Winston.
What has this to do with the way we should explain the workings of natural information-processing systems? See Vision by Marr, pp 15-38. (W H Freeman 1982: PSY CH:M 34; RSL Physiol M 12 b).