Once the Nest Temperature Sensor is set up, you can check the temperature of the room it's in from the Nest app, and adjust your thermostat if needed. This is ideal for multiple story homes, where upstairs will usually be a few degrees warmer than the bottom levels.
If you tend to spend certain times of day in different parts of the house, you can also use the Nest Temperature Sensor to schedule your thermostat based around those habits.