It provides a real time measurement of the signal strength (RSSI) and also allows intelligent data transition capture based on a trigger when the signal strength goes up based on a real message being received. This avoids all the background clutter that occurs when trying to capture 433MHz signals.
The ESP allows capturing both types of data to files and making them available on a browser for viewing and downloading.
It s one of the examples where the accuracy of internal ADC of the ESP8266 is OK as the RSSI already has a degree of uncertainty due to antenna gain. The RSSI measure is still useful as one can see the background level and then check range by seeing the level achieved by a transmitter in different locations.
Code is at https://github.com/roberttidey/RF433Analyser
Construction details at https://www.instructables.com/id/RF433Analyser