With rain pants and jacket., you can count on having extremely wet shoes, as the rain simply drip down the pants and into your shoes. There's also no protection for hands.

A cape helps both. Unless it's very windy, you'll arrive with a small bit of dampness on the toes, but other the inside of your shoes should be dry. The cape can also cover your hands, keeping you warmer and dryer.

Of course, this varies a lot by climate. Where it's windy, capes are a bit of a struggle and in climates where there's a lot of light, misty rain, a good set of pants, shoes and gloves and boots may be needed.

Where I live, I travel with the cape in my pannier. It weighs 8 oz and I can put it on quickly if needed.