For people already with expensive ham radios, the RTL-SDR can be used as a cheap panadapter. A panadapter is device that allows you to visually see the RF spectrum and waterfall being received by the ham radio. There are multiple (expensive) commercial panadapters available, but combined with a PC or laptop, the RTL-SDR will work just as well.
In this video YouTube user akdude47 shows a tutorial on setting up the RTL-SDR as a panadapter for a Yaesu FT-857. The setup involves connecting the IF output of the radio to the RTL-SDR, and putting in some settings into HDSDR.