Do you need sensitive equipment to see if something is totally destroying performance? No. But arguably by definition, you need the ability to reliably measure

Do you need sensitive equipment to see if something is totally destroying performance? No. But arguably by definition, you need the ability to reliably measure at or below the noise floor in order to determine if some emitter is putting out interference that will raise the noise floor (thus degrade performance). Note also that not all measurements are about interference. Antenna patterns and such you just want a more accurate measurement.