they won't help you when you're entering a large foreign city full of one-way streets etc. A navi is ideal in built up areas. With a map you'll have to keep on stopping, unfolding, refolding, making mistakes etc. Not a nice thing to do in rainy weather when it's getting dark.
Maps have their place in the evening when planning the next day, then punch the selected route into the navi and off you go. Makes sure you don't take a wrong turning off a great road.