Here is a longer version of Samsung's Galaxy Note 3 ad called "Sweet Dreams". And by watching this video, I can tell you that I would never ever use a stylus like that, on the run, on the go, walking the stairs and so on... It's too much to fiddle with. A phone should be designed to be used with our fingers, and most preferably, with one hand. It's much easier to use a smartphone on the go then.
I understand that some artists and note takers prefer to use a stylus, but personally I can't see any benefits at all.