First up, Plotting. (or Plodding to those who don't enjoy it.)
Just like those awful reports you used to have to do in high school, having an outline can definitely help. It gives you a clear path to follow, which can be really nice. To oversimplify things, once you've finished plotting, the actually writing is like finishing a dot to dot versus drawing something from scratch.
|I can't wait to see what it's going to be!|
Another nice thing about plotting is you can catch inconsistencies and logical issues before you write yourself into a corner. Again, having a clear path to follow when you write can ease or negate later headaches.
Next up, Pantsing. (or What The Crap Are You Doing? That's Not How You Write a Book! to its detractors.)
Writing fiction is a creative, artistic endeavor, and for the most part, artists don't like being told what to do.
|Or what not to do.|
With pantsing, you can add fun and exciting (or horrible and awful) things to your story as you write, often coming up with things that you might never have thought of if you were sticking to a rigid outline.
Pantsing can also be fun and exciting for the writer because you're able to let the story take you on a trip. It can be easier to stick with a project because you're excited to see where it's going to go next.
Of course, with these positives come some negatives. That's why I really don't think you should stick with just one method. When you start, it's probably best to have at least a rough outline of things that are going to happen. Otherwise you could get well into your story and realize you're lost in happy fantasy land without a good way out.
|...can I go home now?|
But at the same time, you can spend so much time plotting and creating a beautiful snowflake for your story that you lose all interest, and the project dies before it even starts. I think it's best to find a happy medium. A little bit of both works for me, and it might for you. Have at least a rough outline, with clearly defined points you want to make. Then you're not wasting too much time meandering. But allow yourself some freedom to meander as you write. Characters and events and fantastic things are there to be discovered.
I agree with Robert McKee when he said, “We rarely know where we are going; writing is a discovery.” But I also think it's good to take a map.