What's the most important piece of furniture in your home office? A spacious desk? An ergonomic chair? We'd argue it's a door you can close, to minimize the distractions of kids and pets and the temptations of TV and the fridge. But what's the most important piece of hardware? For many home-based workers, even more than their computer, it's an all-in-one or AIO (also called a multifunction) printer—a single device that replaces a separate printer, copier, scanner, and in some cases fax machine.