Hi,
Nothing special at all. It's can be very useful in live sound environments, though.
The desk might not always have HPF per channel and you don't want/need a lot of bass and rumble building up at your gig.
It generally cuts out frequencies outside of that of the human voice, so it is good to use it for voiceover. The Shure SM7B has a plate you can affix over the switch to prevent voice talent from turning the switch off. NPR had trouble with people turning off the high pass filter, and began the practice of gluing the switch in the "on" position.
Appreciate it, gentlemen! I'll start treating them like they were any other high-pass EQ. I've got a couple in my arsenal that I rather like the sound of, but the compare/contrast game is always a good way to kill an hour