The Parabolic Microphone in Phasmophobia is of limited use. In theory it will detect sounds in the distance, making it ideal for larger maps like the Asylum, Prison, and High School. In practice, however, it rarely picks up anything of use. It obviously requires a ghost to make a noise for it to function. However, teammates moving doors, flicking light switches, even turning equipment on and off, can trigger the Parabolic Microphone.
There are some cases, however, where I have seen it work, giving a team a massive advantage of knowing which direction to go. I do keep one in the truck just in case I get the urge to give it a try. Most of the time, however, I abandon it as it gives me nothing. Use it or don't use it. The choice is up to you, of course, and you may just find it helpful.