String values can provide additional information to the dot which is being sent. As a basic example, let's suppose that you are deploying a weather station which provides you the weather status as a string value, e.g. cloudy. In this case, the weather status needs to be sent in the context of the dot.

To learn more of how to display the context of a dot in the Ubidots Dashboard, please check this guide.

mosquitto_pub 
 -p 1883 
 -h industrial.api.ubidots.com 
 -t "/v1.6/devices/my-new-device" 
 -u 'BBFF-Rfcgaxns6HlVb155WA0RhSY85xNDmB' 
 -m '{"weather":{"value": 1, "context":{"weather-status": "sunny"}}}' 
 -q 1