Put one on the wired connection between your computer and router and use it to unambiguously isolate that computer from the internet whenever you want. Or put it between your router (wireless or otherwise) and your ISP hardware to control the connection for the entire house. Sure, you could just unplug the cable, but that’s hard on the connectors, and the switch is faster to use and neater-looking, to boot.
Mark Frauenfelder is the founder of Boing Boing and the editor-in-chief of MAKE and Cool Tools. Twitter: @frauenfelder. His new book is Maker Dad: Lunch Box Guitars, Antigravity Jars, and 22 Other Incredibly Cool Father-Daughter DIY Projects