Or “Why do I need an EQ?” or “How do I prevent feedback?”
Early in my career I worked at a company where I didn’t have a piece of equipment: an equalizer. I did ok on events with one podium microphone and a wireless handheld. But then I had a panel using eight wireless lavaliers, and it was impossible to boost anyone to audible levels without squealing feedback. I made sure management purchased one after that.
You know how when you’re listening to music on a stereo and there’s a “bass” and “treble” control? An equalizer (frequently just called “EQ”) is like that, but much more fine tuned. Instead of adjusting “all high sounds” or “all low sounds” it lets you manipulate very specific ranges.
This is important because for most venues and equipment there’s going to be “trouble frequencies” which can cause feedback, or make things sound unnatural or unintelligible. It’s almost always a good idea to have an EQ on hand. Exceptions might be with a small space and group of attendees or if you’re just using one microphone.