Telling us exactly where you plan to use it would help explain it better for that situation. But here’s some examples:
Mixing: you hear something that is driving you crazy, like excessive bass from a bass player whose sound is like a mud field. If you just have “lows” on your mixer and you dial it downwards , then you get rid of all the bass. And that would suck for low end, the bass player and all his buddies who came to watch. So if you have “low mids” or a parametric mids, then you can dial it down to 100hz let’s say, narrow the width of the frequency to narrow and then dive to the ocean bottom with a boomy frequency and get that mud out of there! A long as the filter is “narrow” or small in bandwidth, then you are leaving the low sub frequencies there to hold down the bottom end. This is the beauty of eq subtraction.
On the other hand, the bass player might have some lows, but it’s all boomy and doesn’t have any real bottom. So you goose up the bottom by dialing that parametric low mid frequency to let’s say around 60hz and boost it with the frequency again being very narrow bandwidth. Now you’re adding some real bottom and not boosting boomy lows.
The beauty of eq boosting in a narrow range because you the a ability to tighten the amount of “Q” or bandwidth.
Or a girls voice over the p.a. Sounds generally thin. If you widen the Q or bandwidth of a frequency range centered around 250 or 300Hz, then you can gently “beef up” the body of her voice. Give it some warmth that way.
Using parametric eq for surgical precision for stage monitoring:
In the real world of playing on stage the singer is trying to hear themselves over blasting snare drums and guitar amps. The singer needs every last db of sound they can get so they can hear what the hell they’re doing pitch-wise. Get the volume up to where they want it and it starts to feedback. You have an graphic EQ but it is sucking the life out of the monitor volume and the singer says it sounds muddy. So with a parametric eq you can find the offending frequency, and narrow the Q down to very narrow and “notch” just that frequency while leaving the others intact. Try being chained to a monitor console with a national level deaf “artist” screaming at you for more monitor and using high end graphics or parametric eq can save your butt from ego driven rants and stink eye. Been doing that for 35+ years .
Depends on what you’re doing but there some really bad sounding eq’s out there and some really high end ones too. Using a bad eq to flavor things can lead to worse sound rather than fixing sound. Boy I have a million stories about that

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