They would be very useful for people who want a simpler way of radar systems or multiple viewpoints. They don't have to be controllable, just another eye to see from. For example, if you wanted a radio-controlled car, you could be able to see its view and your own view in two separate windows.
A radar control could have specific options such as type color-coding and range, along with background color.
It's not necessary, but it would be easier.