Subject Report

The subject report is a way for you to keep track of all your surveys.  When creating a survey, you have the option of creating multiple copies of the same survey (a Project).  For instance, if you had 6 managers (as shown below) you could have all of their employees take different surveys- each employee taking the survey for their manager.  Each survey therefore has a Subject- the person or thing that the survey is about.  This page simply lets you know the status of each survey in your Project. 
Benefits: The subject report let you know quickly at a glance the vital statistics of each of your subjects.

Respondent Report

The respondent report displays information on the status of your survey's respondents.  It tells you how far each respondent is in the survey, and when they started and completed the survey.  If you have chosen your survey to not be anonymous then you can click on a respondent's name to view their answers to the survey. 
Benefits: The respondent report allows you to check on the progress of your respondents towards completing the survey.  It is an easy way to see who has completed and who has not yet started your survey.