It is useful to find which part of a device is emitting a specific frequency. The part emitting the frequency may not be the original source of the energy but it is part of the transmission path.
The XL2 with Spectral Limits/Noise Curve option allows you to listen to the sound through a 1/1-, 1/3-octave, 1/6-, or 1/12-octave filters. You could but the XL2 mic on a mic boom pole https://www.bhphotovideo.com/c/product/770230-REG/On_Stage_56791_MBP7000_Microphone_Boom_Pole.html to get the mic close to different potential sources.
You could the listen to bandpassed sound through headphones as you move the mic from potential source to potential source.
To use the feature:
The picture got left off the initial post.