Each method has staunch supporters. I once read an article about Ken Follett that said each novel started with a full synopsis - full being about 300 pages. Stephen King, on the other hand says that he sets out with an idea and sees where it leads him. For myself, I'm somewhere in the middle. I like to know a few key moments that I can aim for - woman falls in love, woman falls out of love, for example - but the how and why and what are all mysteries to be solved along the way.
I've only once tried fully planning a novel, and the result was that, although I loved all the planning and plotting, I never actually wrote it up. It lurks in all its colour coded wonder at the back of the writing cupboard, having absorbed all my inspiration into its perfect plan. For me, extensive planning was a substitute for actually writing a novel.
But, in the end, it doesn't really matter how you change the duvet cover, so long as the bed gets made.