Most people switch on the guest network once, read the password aloud to a room full of visitors, and never open that setting again. I treated mine the same way for years. Then it clicked. My guest network is a whole second Wi-Fi, fenced off from the main one, with a name and password of its own. Devices on it get to the internet and nothing else. They never see my primary network, and I decide what's allowed to join. When I wired my house for gigabit, that spare network quietly became one of the most useful tools in my router settings. Here are four jobs it handles that have nothing to do with hosting anyone.