What is the use of a single ultrasonic signal? The EV3 ultrasonic sensor has an advanced mode that includes an option to use single or continuous sensing as described in the Help page:


  You can choose whether the sensor sends a single ultrasonic signal or continuous signals with the Measuring Mode input.


What is the purpose of a single ultrasonic signal? In what situations may the sensor need to send a single signal?
I'm not an EV3 expert, but my understanding is that continuous mode stores results into a buffer that can be read nearly instantly. Single mode will need to wait to hear a ping back before reporting results.

Continuous mode will give you a faster response time. However, if you are using a number of ultrasonic sensors, they may interfere with one another, and using single mode should prevent this.