Often knowing the direction and intensity of consumer / public opinion can highlight what the specific issues are. 

For instance, knowing the level of consumer confidence is relatively meaningless in isolation.  Knowing how consumer confidence has changed in the last month / six months / year shows the direction of opinion which can then be compared to economic events.

A repeat survey is one that repeats at regular intervals, usually, daily, weekly, monthly or quarterly.   Repeat surveys are sometimes also known as continuous or tracking surveys.

They can be used to understand changes in awareness of advertising, brand perception, consumer confidence or a range of other questions over time.