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. 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 the why and the 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 writing inspiration into its perfect plan. For me, extensive planning was a substitute for actually writing a novel.
Other authors can't imagine embarking on writing a story, let alone a novel, without having it plotted out in great detail. I remember when I was speaking at my first writing conference and talking about my non-plotting approach, immensely successful romantic novelist Kate Walker - who was also on the panel - was amazed with my levels of re-writing. She didn't have time for all that faffing around, she was too busy with the story telling.
My method does take time, but there you are - it's my method and so far it seems to be working out. In the end, it doesn't really matter how you change the duvet cover, so long as the bed gets made.