This past weekend, our LUG did a Iron Builder event. We had 30 minutes to gather up parts and build a MOC (see the rules), incorporating a 'mystery' piece -- for our event, the mystery elements were clown hair. :)
When I first saw the hair, I thought I'd try to create a flowering bonsai tree. I gathered up a bunch of green plate, brown bricks of various sizes, and Technic pieces. I know time was short and the available pieces for build were limited. I wasn't going for perfection or a refined MOC -- I wanted to build it quickly, with some whimsy, instead of it being meticulously planned out.
I didn't win, but I'm okay with that. :) For me, this was to build something quickly, not over think it, and have fun.
And to be honest, it is a fun contest!