No, when you aren't talking into the Mic, the noise floor will be below some threshold. You can use the expander to quiet the Mic when you aren't singing below that threshold.
This is a great way to control feedback when the band stops. Sometimes when the band stops, feedback can occur. So, try it. :-)
I might use high pass on the EQ to reduce rumble. I would not usually try to EQ out noise above 80, except notching for feedback control.