The user wants to leave an opinion or evaluation about an object, person, place or thing. Quick opinions can be captured using ratings or voting ("thumb's up," "I like this!"), and more in-depth evaluations can be captured as reviews.
A product or website needs to present ratings and reviews with a variety of informational elements.
A user wants to quickly leave their opinion on an object, with minimal interruption to any other task flow they are involved in.
The user wants to promote a particular piece of content in a community pool of submissions.
User wants to share her opinion with others about an object (place, person, thing) in greater detail than a simple rating.