Those who are planners by nature will tend to work out everything about their books - not just the important stuff, but also the details. They will sit down and write a thorough plot summary and even plan their chapters. Authors who write chapter plans might even come up with each chapter title before they write the book. When writing the book, they will follow their plans carefully. Some planners even know how long their word count is going to be. I personally never have a clue how many words my books will turn out to be, so this has always fascinated me.
Other authors prefer to write a book outline, sort of like an essay outline. They will decide what the main events in the book will be. Then they label each event with numbers or letters and include sub points beneath. This outline can still become very long, but is an excellent scheme if you want to get the general idea of your book without feeling like you have to write out a full plan.
Panning is my forte when it comes to writing. I used to be a planner, but my characters would wreck all my plans within approximately two chapters. This literally used to happen to me all the time. I would write chapter plans and full plot summaries. Within the first quarter of the book, someone whom I hadn't anticipated killing off had just died. Someone's long lost family had shown up. An entirely new character had just walked in and several friends had given up on each other, meaning that a plan involving all of them working together was never going to come off well.
These scenarios led me to become a panster. Clearly I couldn't control my own stories. So I gave up. Nowadays, I tend to write down a few things that I know will happen in the book. Normally when I decide to write a book, I will have two or three scenes in my head that I think are truly epic and exciting. Then I start writing the book. The story around these two or three scenes just unravels slowly and I follow the characters in what they want to do. Normally my villain always has a goal. Lately, my protagonist has been good in this area as well. Hence, they just carry on doing what they want to do, and the story evolves through their actions.
When I edit, I have several more ideas for how I want scenes to link up. I write notes and tend to have a bunch of loose ends that I want to tie up. But I'm always happier with the book when I've let it pan out than when I've planned it. The reason for this is that my characters simply have the space to live and breathe. They are doing what real people would do rather than what my plan had them doing in the first place. They come across as real constructions (I hope).
Are there cons to planning? Absolutely. Are there cons to panning? Yes indeed. Here are two lists.
Cons to planning
1. Your characters act irrationally because they're doing what the plan said, not what human nature dictated.
2. Your book comes across as lifeless because things aren't happening organically or naturally.
3. It is harder to see faults in your work because you've only ever seen it one way.
Cons to panning
1. Editing will become your worst nightmare... literally. You will have to carve a plot out of junk.
2. There will be many loose ends to tie up, and no answer is the right one. Because you've "panned" your book, you're able to see it many different ways.
3. Your book will come across as nebulous and nonsensical if you're not careful.
Which road should you take as an author? That is entirely your choice. I would suggest that a beginning author tries both methods at some point. Maybe it wouldn't work with two entire novels. Your first novel can feel like a big enough effort. Try it with two novellas or two short stories instead. Find your style. Be aware of the pitfalls outlined above. And lastly, do not be afraid to write because of the risks. Never be afraid to write, because you will never get anywhere with your story (or anything for that matter) if you let your fear define you.