More importantly, a smartphone or GPS can quickly give you the best route to your desired destination and talk you through it while you're driving. You can't be reading maps and driving safely at the same time. Plus there's a detailed street level map for you wherever you happen to be. Just finding the correct map out of a whole book for the street area you wanted was a pain. And if you travel to any city, you'd have to have a map book for there too. With a SP, it's all there at your fingertips.
People who haven't actually used one don't realize how well and how seamless it works. You can google for a business, find it, then with one more tap, place a call to it or with a couple taps start the navigation with voice driving directions to it.