Today is the last day of my seventh NaNoWriMo. I started participating in this challenge back in 2006, and I've done it every year since, though I've failed to reach 50K words more often than not. Although I'd won last year, and again in August when I participated in the summer session ("Camp" NaNoWriMo), this November I failed to reach my 50K word goal.
However, I don't consider this NaNoWriMo to be a failure.
Since I was finishing the novel that I'd gotten halfway through in August -- I figured 50K was a good halfway mark for this novel, at least by the way it felt -- and since I'd lost the thread of the novel in September and October, the biggest success this month was getting me back into the novel. The hardest thing about writing a novel is picking it back up again if you happen to take a few days or a few weeks away from it.
The other thing that NaNoWriMo did for me this year was to force me to fill in my outline -- so, even though NaNoWriMo is leaving me with more work still to do, I know where I'm going with it now. Having the rest of the story in your head always makes it easier to keep writing.
And the final thing that NaNo has done for me in 2012 was to help me figure out more of the series outline. This novel is the second in a planned series (I wrote the first book last year and am working on revisions). I figured out gaps in my plan for the series, and solidified plans for future books, too. It's all coming together, piece by piece!
And that is how NaNoWriMo can help you, even if you never make it to 50K words!