Answer to Question 1
Sensible heat causes a change in the refrigerant temperature while latent heat causes a change in the refrigerant state. Much less refrigerant has to be circulated if the refrigerant's latent properties are used rather than its sensible properties because refrigerants absorb much more heat while changing state than they do while changing temperature.
Answer to Question 2
Refrigerant is the fluid used in a refrigeration system for transferring heat. Refrigerants in mechanical refrigeration systems do this by changing their physical state. They absorb heat by evaporating from a liquid to a vapor; they release heat by condensing from a vapor back to a liquid.