The ability to display labels onto map locations (and more recently filled maps) has always been present -- simply drag and drop a field you wish to use as the label onto the Label shelf. However, in many circumstances there may simply be too many labels that appear on the map to obtain useful information.
This document will demonstrate how to display labels on a filled map only when a particular criterion has been met (without manually modifying your marks). A measure field called Demand is used in this example, though other measures such a sales, weight, population, etc. can easily be used. This same process can also be useful when conducting sensitivity analysis.