I've been using PlotJuggler for a good couple of years now and it's one of the go to tools for debugging robotics systems for me. I'm sure it had saved me a good couple of days of my life!
An example of the top of my head for debugging: the robot I was working with was not very eager to turn on the spot, by plotting commanded angular velocity vs angular speed from wheel odometry I was able to see that commanded velocity was fine and the issue was on the motor controller level.