One of the complaints you might have about common alternative sleeping arrangements such as futons, sofa beds, and air mattresses is that they're just not comfortable or supportive. With a Murphy bed, your guests won't have that problem. They are the same size as a standard bed and they offer a thick, supportive mattress for the ultimate in comfort.
For you, the benefits go beyond having a guest bed at-the-ready. Your wall bed will contain shelves, drawers, and/or cabinets that will add storage space to the room you add it to. By day, the unit sits against the wall, taking up minimal space, so you can put it in your den, playroom, home office, library, living room, or anywhere else that you'd like to be able to add storage and also host guests.