Per ISU Communication No. 1629 (published in July 2010), the contrasting objectives are:
Originally Posted by Alba
ISU World Standings
To present an objective and accountable standings system for all skaters in Single & Pair Skating and Ice Dance during a particular season which takes into account the results of the preceding two seasons ensuring that skaters who were unable to compete for a certain period of time remain in the World Standings and are considered according to their true basic competitiveness. The ISU World Standings are used as basis for all draws in ISU Events as well as one of the skaters selection criteria for the ISU Grand Prix of Figure Skating and other ISU Events designated by the Council.
ISU Season's World Ranking
To present to the public at large and the media, an acceptable and accountable standings system of all skaters in Single & Pair Skating and Ice Dance for the current season giving an indication of the current actual competitiveness of the skaters [emphasis is in the original ISU document].
As this ranking order does not protect skaters who were unable to participate in events of the previous season(s), only the World Standings System as introduced under paragraph A. of this Communication shall be used as the basis for the draws at ISU Event and as a critieria for the skaters selection for the ISU Grand Prix of Figure Skating and other ISU Events designated by the Council.
Link to the full Communication (five pages):