I find that I'm able to convince people of things and explain abstract concepts with much more ease than other people. This holds true even if I don't fully understand the idea I'm explaining. Something about being able to "mold" the space in front of me lends another dimension to weave the fabric of language around.
As a personal anecdote: I won the Marconi-Samueli Award for an app I built when I was 14 called MathSuite. It could parse algebraic equations and yield a result, and it did so offline (think Wolfram Alpha). I'd built the thing from scratch, and on the day of presentation, my computer had crashed and I couldn't ship a version of that app that would run.
Somehow, I convinced the judges of the veracity of the screenshots and claims on my presentation poster, and explained to them the potentially huge ramifications of my app, without being able to demonstrate it working. One judge commented that I had a "very expressive and mature style of explanation" — really, I think my hand gestures were a huge part of it.