Actually, in full it reads: "1/8” TRS input with 5V power for use with stereo electret microphone (microphone included)". I think the concern is that this input will only be a mic input, not selectable for mic or line. So it might be routed no matter what through a mic preamp with additional gain, more gain than would be wanted if running line in, or even if getting a really hot mic signal from taping a loud PA.