This option allows you to have an "Quota" based Survey.

Example Scenario:

Say you wanted to survey equal amounts of "Male" and "Female" respondents. You could set up Branching on the "Male/Female" question and have an OverLimit Quota Jump to a "Thank You -- But We have reached the Limit" Question if either males or females who are responding to the question have exceeded the required number of responses that you are looking for.