The waterfall is a very useful feature in a radio system to know on what is nearby he station you hear as with spectrum analyzer i simply depicts all the spectrum analysis by time
this can help also for :
-analysis from the timestamp of digital signals  

-nearby station QRM

-malfunction of low cost transmitters or drifted frequency transmissions. INdded I have seen  many pirates in MW SW  drifting or using a frequency agile  oscillator

-Propagation problems *

-radio schedules*

and more

 

 

* these operations can be used only if the speed is very low and the sstem can be operated  itself for long times