I do think the advice is sound for new/novice writers because novel writing is a daunting task, and to keep everything straight (characters, plot, subplot, relationships, etc.) can be mind boggling. So keeping notes and doing an outline would help someone starting out, just to keep their heads straight. For a seasoned writer, it might not be necessary, depending on how the person works.
Also, some genres may be better served with outlines: Mystery? Science Fiction? Fantasy?
When I started writing my first book, I was relatively new to the whole novel writing thing. So I did do a little bit of outline in the beginning, just to help me keep things straight. But I found myself deviating from that outline all the time (not a crazy mesh of chaos, mind you -- just that my characters took me places I hadn't thought about...) and eventually just abandoned the outline and wrote without one. Everyone who read it, including my editors and a couple reviewers, told me how well the story flowed and the characters came together. So I must be doing something right without having an outline...